Edit existing unit animation

[Oceans14 Profile]

Hey guys, I'm having some trouble editing the stock rifle reload anim. I brought it into xsi and made the adjustments, but whenever I play back the anim the hands and arms are reset to before. I'm setting the new key frames but for some reason I can't delete the old ones, which I suspect is causing the problem - I select the key and use the menu to remove it, but nothing happens.

Thank you for any help!