Heres's an easy way to beat Aragog without getting hurt. When you enter the place where Aragog is, there will be shinning blue/purple pillers against the wall. Cast a spell at a piller and it will shatter causing a couple of big spiders will appear. After stunning the spiders they will disapper. Repeat this until all the pillars are gone. Then Aragog will come down. When he gets down, run sideways one way and keep attacking him. He wont be able to attack you.