Painting outside trims

MRSTITTLEMOUSE

I live in an early victorian house and need to paint round the bay windows,doors and roof trims,window ledges ect.It's already painted and some of the paint is lifting and bubbling as it's old.Can anyone offer advice on how to prepare the surface ready for the actual paint.We're frightened to just go ahead and scrape off the loose paint incase we do more harm than good.
Also we are using the same shade as already on so will it need undercoated first with something to protect the surface or once prepared do we just go ahead and paint.Thanks.

nickj_2

if the paint is brittle it would idealy need to come off - you can use a hot air stripper - don't do the putty as this will crack the glass ,
then sand down and prime - u/c and gloss as per intructions on tin
https://www.dulux.co.uk