There is a tutorial on that in the tutorial area on gametechmod webpage.
The closest description I can give
Before you start, back up your bot file
1. First, open the bot file with notepad++ (Unix Format). This is important as some other text edit programs (like ultraedit or pspad) will mess up your bot file.
2. Scroll down (or use the search function) to find "chassis"
3. Now, about 12 or so lines down there's a number with a lot of decimal places (between .44 and 1.32), copy this number. To make sure you got the right number, there's also another integer to it's right (don't copy this too by accident), and a "true or false" right below.
4a. If it saids false right below this number, all you have to do is change the number describe above (this is the case if you use one of the auto create shape function).
4b. If it saids true, it means you created the chassis using custom define point (which also mean that the game have to record your height separately), use the search function and find all the instance where this number shows up, and you will have to change all of them **They should all be in one cluster anyway**, making it easy to find.