If you really want to increase your vertical jump in just 4 weeks the best way is to get excellent vertical jump program.

There are many programs online that can help you to learn how to jump higher but you should know that the problem with most vertical jump programs (besides outrageous claims) is that they are not progressive and comprehensive. They only focus on training one area of your body to improve vertical jump.
When you choose your vertical jump program it’s very vital to choose one that really targets every facet of vertical explosion.

Check this helpful website about the best vertical jump programs.
You will find there reviews and comparison between the different programs. Here is the address:

http://www.jump-programs.com/Best-Vertical-Jump-Programs.html

Hope it helps…
Excellent luck

“Start every workout by warming up your muscles and then doing extensive leg stretches. Because you’ll be building muscle fibers that are used for explosive activities such as jumping, stretching is of the utmost importance.

2. Jump rope for its brilliant cardiovascular conditioning. This step should never be skipped, as it will be an vital contributor to your results.

3. Incorporate sprints into your workouts. This builds muscle, which will add to your jumping ability.

4. Run stairs on your toes. Start by running up a flight, one step at a time. Walk down and run back up, taking two steps at a time. Repeat as many times as you can manage.

5. Do sets of elevated jumps (see the next section).

6. Do sets of explosive jumps (see the third section).

7. Do sets of double jumps (see the third section).

8. Rest your legs at least two days a week. Results will come from sustaining the exercise program, not performing it aggressively for a few weeks and then slacking off.

Elevated Jumps
1. Start by placing a step bench or platform on the ground (many health clubs have a platform for just this purpose).

2. Stand on the platform, then jump backward onto the ground, concentrating on landing softly.

3. Jump back onto the platform immediately, with a bouncing motion.

4. Complete three sets of 10 repetitions. Be very careful when performing this exercise, as there is a potential for injury. Question a trainer or spotter to help.

Explosive Leg Jumps and Double Jumps
1. Position yourself for an explosive leg jump by facing a secure platform and placing your right foot on it.

2. Jump as high as you can, concentrating on exploding off the right leg. Scissor your legs once in the air, then land with your left foot on the platform and your right foot on the floor. Gather yourself and explode upward again, this time off the left foot.

3. Do three sets of 10 repetitions, resting for about 30 seconds to 1 minute between sets.

4. Do a double jump by jumping as high as possible with both feet from a stationary position.

5. Jump again immediately upon landing, using less effort.

6. Repeat until you’ve accomplished three sets of 10 jumps each.
Source(s):
ehow i hope this helps!” i did most of this stuff and i increased my veritical by 20 inchs

2. Jump rope for its brilliant cardiovascular conditioning. This step should never be skipped, as it will be an vital contributor to your results.

3. Incorporate sprints into your workouts. This builds muscle, which will add to your jumping ability.

4. Run stairs on your toes. Start by running up a flight, one step at a time. Walk down and run back up, taking two steps at a time. Repeat as many times as you can manage.

5. Do sets of elevated jumps (see the next section).

6. Do sets of explosive jumps (see the third section).

7. Do sets of double jumps (see the third section).

8. Rest your legs at least two days a week. Results will come from sustaining the exercise program, not performing it aggressively for a few weeks and then slacking off.

Elevated Jumps
1. Start by placing a step bench or platform on the ground (many health clubs have a platform for just this purpose).

2. Stand on the platform, then jump backward onto the ground, concentrating on landing softly.

3. Jump back onto the platform immediately, with a bouncing motion.

4. Complete three sets of 10 repetitions. Be very careful when performing this exercise, as there is a potential for injury. Question a trainer or spotter to help.

Explosive Leg Jumps and Double Jumps
1. Position yourself for an explosive leg jump by facing a secure platform and placing your right foot on it.

2. Jump as high as you can, concentrating on exploding off the right leg. Scissor your legs once in the air, then land with your left foot on the platform and your right foot on the floor. Gather yourself and explode upward again, this time off the left foot.

3. Do three sets of 10 repetitions, resting for about 30 seconds to 1 minute between sets.

4. Do a double jump by jumping as high as possible with both feet from a stationary position.

5. Jump again immediately upon landing, using less effort.

6. Repeat until you’ve accomplished three sets of 10 jumps each.