I had to trim my neck seal and missed my first planned dive with my seaskin. Got suited up, was getting rest of gear on and stood up and almost blacked out. Trimmed one ring and suddenly I could breathe and didn't feel like I was blacking out. As others have said, sharp instrument(I used an xacto knife with new blade) and take your time. I used a 2 liter bottle in the neck and just rolled around the neck in one motion. Honestly I was scared to death thinking I was going to slip. Coat me the one dive but better than actually passing out in/under water