Its a long time since I had a 4G (or a car with a distributor for that matter) but normally the horizontal clamp plate stays locked onto the distributor body, the vertical locking bolt is loosened and the slot in the clamp plate (plus distributor) moved below it. A marker pen is used to mark the start and finish positions so that you can return to the starting point if it didn't improve.
This sounds easy, but actually you may have to slacken both clamp bolts, hold the distributor firm (no movement) and adjust the clamp plate so that there is some available adjustment in the slot before you start.
How much movement per adjustment ??? Small amounts only (i.e. half the width of the vertical lock bolt's stem). Only adjust one thing at a time (i.e. timing or carb) or you won't know where you are
How to judge the result ??? I would start by advancing the timing a bit, if you overdo it there will be pinking - which is bad. If you over retard it the exhaust pipes may turn blue - which is worse and less easy to fix
Aim for smooth running, clean acceleration, no hesitation at speed and decent fuel consumption and plug colour. If you achieve all of this . . . Tell us how
My avatar shows the late Len Rich in 1970 with the bike I now have - a 1958 Ariel VH