First thing to check is the level of the transmission fluid. It may just need to be topped off. Take a look at your owner's manual on how to check it and what type of fluid it takes.
If this is not the problem then you should have it checked out by a certified technician. It may need an adjustment or there could be something that needs to be repaired in the transmission itself.
〉 Answered on May 5th, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines