I used a drill and went into the punch till it was at bottom. I pressed them off and used standard Bulgarian ak74 parts to replace them. I saved the originals which could be welded and re used. My Russian is a 1988 unfired kit.
On my Saiga I used a end mill to cut part way through the spot welds and then with a die grinder, cut a groove the length of the front sight on the bottom until I could get the the blade of a screw driver in it and twisted it until it cracked. Use the end mill and pry with a screw driver until the welds break.