Good advice : you can repot maples almost any time, provided that you cultivated them. But for a tree you've bought from a nursery, you don't know what the roots look like, how it was cultivated (soil, ferts, etc) so I would just slip-pot it in a wider but not deeper pot, adding some coarse pozzolane (lava rock) or pumice to give more "air" to the roots until next spring when it has thrived. I would just select a few branches in late June when it's at its top form.