If you have one of the regular ones (non USMC) there are several methods. You can lift from the bottom of both sides while pulling out and away from the barrel, you can put a piece of stout cord through the top of the cover and pull it off that way, some folks pry from the front or the back. All of these methods will mar the barrel.

If your rifle has a USMC front sight cover you probably have a job for a gunsmith.

On M1903 rifles I just leave them on since they don't interfere much with the sight picture. On M1903A3s I remove them before shooting.