Varnish and paint on a shed…..

We bought a really good shed about 8 years ago, decided to varnish it with Sadolin and have redone it (nearly) every year.

The garden has now be landscaped and we would like to change the colour of the shed, how easy is it to paint over varnish? Would we need a special paint?

Any info appreciated, it’s a job I’d rather do myself at the weekend rather than get the pro’s in!

Cheers