First, skydive your wingsuit. If it fits and flies well, great news. No tuning is needed.

If you sense that it could fit a little more tightly, then it is possible to tune it. First, put your suit on without your harness/container system.

Open the main body zippers down to your hips. Then open the access zipper and locate the cinch. Pull the cinch until you start to feel a small result. Usually, cinching it until you just barely start to feel a difference in the suit, is enough!

DO NOT OVERTIGHTEN. CINCH ONLY 10-15 CMS AT A TIME.

Repeat this process for the leg wing. Unzip the left body zipper down to your mid thigh. Open the leg wing access zipper and cinch each side until you start to feel a small result. Again, DO NOT OVERTIGHTEN.

Overtightening the cinch system is easy to do, and makes everything worse than it being loose. If you overtighten it, the suit will be much less comfortable to sit in the plane with, and you will also deform the wing profile.

Read the manual.