What kind of light is it (brand and model)?
There's only so many ways of sealing a light. The posted picture doesn't really let me have a close enough look to tell anything for sure.
Either it's glued and isn't meant to be taken apart or the head unscrews or it has a bezel that unscrews (or both)...or if it looks like those don't apply then it may have an o-ring in front of the lens that you take out first and then take the lens out and then take the reflector out from the front.
I can't think of many other possibilities.