Dont say go to the website because i tried it and it diddnt work.
Then I can't tell you how to update it

- Go to trem.tjw.org/backport/
- Navigate to your OS and download the Tremulous binary
- Replace your current Tremulous binary with the one you just downloaded
If you need more help (such as finding where the executable is hiding), start with the Search button ^-- up there, and if you can't find it post here and ask. But for updating a client, it's been posted in the boards here quite a bit so you should be able to find what you need.