You can take the GRE I believe up to 5 times a year. HOWEVER!!!! (yes, this is a big however), GRE reports every score you submit, so do your best in as few tries as possible, because schools will see every score you get. The worst thing to look like is someone who just keeps taking in it hopes of a higher score.
Also, keep in mind, if you feel you did poorly on the GRE, you can elect to not have the scores reported, and it will be as if they threw out your exam right after you took it, no one will know.