Most lenses will have a decorator ring with the name,focal length & aperture information. This ring unscrews anti-clockwise.
I have a selection of rubber stoppers(bungs?) to remove them with. Using the edge of the stopper, hold it against the ring & turn it. sometimes you will have to do this at different points around the ring. Occasionally a drop of alcohol around the edge of the thread may be needed. Don't use too strong a solvent, you don't want to start separating elements.
OK now you have the ring out. Canon FD lenses will typically have a retaining ring held in with three screws for the front element.
Other brands may have a hidden ring with spanner notches under the decorator. Some you will have to remove an outer ring that has lens info on it, these often have set(grub) screws that need to be loosened.
Rear groups are usually screwed into the rear barrel with a spanner.
Microtools has a pretty complete collection that you can look at online & possibly find a source in Britain.