WAIT Don't start immediately.
I'm surprised you haven't found the pruning page on this website, but it says 'Overall, the early spring or late autumn is the right time to structure-prune a tree (just before and after the growth season).'
Make sure the timing is correct before you do anything or it could seriously damage your tree. Here in the UK (you're in Scotland, right?) spring starts in March, so wait until then before structural pruning (the 'official' name for shaping the tree).
Ed
oh, right:
www.bonsaiempire.com/basics/styling/pruning