Need help with Irfanview

I have no trouble resizing to fit in posts but i cannot for the life of me figure out how to cut just the image i need (like a weapon) and fit it to the screen. I can remove the backround but im left with a large screen and a small pic of my weapon or item. Please help!

Come on someone must know this????

I'm assuming get some picture editing and erease part of it lol... or cut it out and save it or something... use picassa...

ugh, alright ill try picasa