Feed him once a day. Change his water once a week if he's got a 5 gallon, twice a week if he's got a 2 gallon, every day if it's any smaller than 1 gallon.
To change his water DON'T remove him from the tank. I used to do that when I didn't know any better... don't bother cleaning all the sides and everything unless it's really gunky and gross and you want it to look better, cause the betta doesn't actually mind that. A water change is usually 20-50% of the water. You use a siphon hose though I guess if it's really small you could just use a cup to remove and replace water. Make sure you remove ALL the water you are removing before replacing any, or else you'll be removing water you just replaced, and if you do the math, you're wasting lots of fresh water that way. Only add water at the end.
The point of water changes is to remove fish wastes from the tank. The smaller the tank is, the more you need to remove.
Personally I wouldn't put him in any smaller than 4 or 5 gallons so I would have just said once a week, but I know lots of people put bettas in smaller containers.
n2existance: Food packages tell you to feed lots of food so that you buy more food. Fishkeepers who have kept bettas for a long time will usually tell you to only feed once a day, not twice or three times a day unless you are doing it for a particular reason, like trying to condition them for breeding. And 3-5 pellets is too much. I'd say 2-3.