m900 Headlight

I've got a lot of fogging on the inside of the headlight lens - I've taken the headlight apart to clean it out but couldn't get the lens off of the reflector. I didn't want to force it in case it's a sealed unit - anyone know if these are supposed to come apart?

Also, can I do a straight swap from the existing H4 bulb to a more powerful halogen lamp without changing anything else?

Cheers

G