When you can't retract the foreskin easily with your penis erect. I had this problem and I went for a circumcision operation about six years ago. Simple op and I'm glad I got it done. A circumcised penis definitely looks better and remains cleaner.
You are given a local anaesthetic and a surgeon cuts the extra skin and stitches up the rest. It takes about two - three weeks to heal. Glans will be sensitive but after a while it will be fine.