Can I up power my Armex 10 avenger air rifle myself. If yes can anyone tell me how cheers?

First of all, find out what the legal power is where you live. You don't want to break any laws. Then I suggest you contact ARMEX and find out if it is possible, or search the web for "air gun tuners." these are people who modify airguns for a living.

See the link below for ARMEX