How to change what computer your iphone is linked to without loosing everything?

I have an iphone 4 and I'm stuck it it for at least another year. I got a new computer for my birthday because my other one was extremely slow and stuff. How can I sink my phone to my new computer without loosing everything?

Sync is per computer. You will lose all synced content. So your music, movies, apps and TV shows will have to be either redownloaded or resynced.