My son was a real wriggler when he was getting his nappy (diaper) changed and would sometimes scream long and loud in protest.
I had a routine for nappy changing which made things easier, and I kept everything I needed in a change box.
Before I started I made sure I had everything laid out and within easy reach. I made sure that anything that needed two hands to open or unfasten had already been opened/unfastened before I started.
To stop him wriggling or kicking, I held his ankles in one hand, and raised his legs up to give me easy access. He did wriggle, and it wasn't always easy to hold him, but it was the only way I could manage it, and it did mean it was over much more quickly.