The chrome ring is held on by a small cross head screw usually close to the 6 o'clock position, it may require a stubby screwdriver (or right angle) to get at it.
The lamp unit is removed by taking out the (I think 3) retaining screws, be careful you do not touch the lamp position adjusting screws. A piece of white masking tape can be used to mark the glass unit's position in the headlamp well to aid in reassembly.
You may find that there is a sticky rubber gasket/foam which will need to be carefully separated.
Place a towel/blanket to rest glass unit on while you pull off the rear H4 connector and replace bulb.
