The nameplate retaining ring unscrews, and the lens elements come out. Later models, I believe have notches for a lens spanner. Earlier ones like yours come off with the appropriately sized rubber friction tool (I forget what they’re called - looks like a rubber socket)....or you can improvise with the right size socket from a mechanics tool set (or anything rigid the correct diameter), and a rubber band. They usually come right off, but some may need extra attention, like a very, very minuscule partial drop of light penetrating oil in the threads....hope this helps. It should easily come off. I once removed one with 2 soft pencil erasers.
