put it inside the GDB folder in kitserver, edit the map.txt and set the correct folder for the team you want to use the kit.
example:
0,"National\Europe\Austria" (*kitserver folder*\GDB\uni\National\Europe\Austria)
If you want to change kit, change the line as described below and put the new kit in a folder as described below.
0,"National\Europe\Austria2" (*kitserver folder*\GDB\uni\National\Europe\Austria2)
EDIT: I have no idea why there's space in Europe, it's not supposed to be there.