don't try the linux instructions on how to partition. instructions aren't concise or comprehensive. you'd have to read a bunch of different posts in order to find your way, and in the end still probably mess up -.- true story lol.
aside from using the test mode app, you can boot into recovery mode by holding home + menu until the bar reaches the right.
i personally used acronis true image to repartition. back up the entire disk first. this makes it easier as you don't have to work with the limitations of not being able to resize the data partition since its ext3. my memory is blury but i think what i did was delete system and data, created a new blank ext3 partition with size of my choosing and then simply restored the data partition on top of the blank. then restored system to the remaining free space.