AGV have several types of Visor so the following is for the Race Visors as fitted to the AGV TiTech sat beside me in the office
Press up little plastic catch on the RHS of the visor as you're looking at the Lid head on. This lets you pull the visor more open than usual and will let it pop off the catch on that side. Now gently close the visor as it's only attached on one side, it'll be able to go down further than normal & come off
Hope this helps
Jambo