2 person job, hold the window from the outside, a couple of those dent puller/glass pane holder suction jobs are ideal to stop it dropping, then from the inside unclip the plastic covers over the fixings & unscrew , you'll have to force the plastic trim out of the way a bit (may be an idea to warm it a bit with a hairdryer if it's cold & a bit brittle to stop it cracking?), especially on the rearmost fixing, then it just lifts off, simplez

You can't polish a turd - but you can roll it in glitter.