Download and extract the 0.3x server package in your server's folder.
If a dialog pops up with 'Allow overwrite' or something like that, press Copy and replace.
After that's done, recompile your scripts.
Congrats, you've updated your gamemode (and other scripts) with the latest includes of 0.3x!
EDIT: here's a tutorial on how to update old scripts:
Updating your sa-mp server and scripts