DO NOT SIMPLY WHACK WITH A HAMMER. you'll risk torquing the steel and then your accuracy will go to crap.
First, On your ak, there will be pins that are driven into the steel between the barrel and the front sight post. remove those pins with a punch, then align the sight, then purchase some steel tube stock in an apropriate width (slightly larger than the previous pins), drill out a larger diameter hole using the previous holes as your guide, and then cut your round steel stock to size and hammer into place.