Uninstalling
means deleting the program (and some other files).
By far the most storage hungry part of GB are the loops, so you might just delete the corresponding folder: HD/Library/Audio/Apple Loops.
If you want more free space, delete the Instrument Library: HD/Library/Application Support/GarageBand/Instrument Library.
That will leave GB without loops and instruments, but still capable of recording audio.
If you want to get rid of GB completely, do a Spotlight search with "garageband" and delete all the files that come up (that includes the program).
And please don't write in all-caps, that's considered shouting (and hard to read).