Painting and sanding wndow frames outside the house

[RadarBailey]

I'm in the process of having some new windows put in. The wood which surrounds these window's is also being patched up as some of it is rotten. Over the years the previous owners have just painted over the old paint. Some of which must've flaked off as the surface is uneven and looks a mess. Should I sand it all down? and if so what kit can I hire which will make the job mush easier ? They're bid windows. Do I need to do anything to the old wood before I paint it?

Thanks

 

[joe-90]

Get rid of the old wood while you've got the chance.