Take a bit with you but you can easily change money in the resorts. Obviously take care, as with any resort, where you change it but we found it easy and reasonable many times
If you take sterling with you make sure your notes are newish no rips or writing on and no scottish ones. Change at your hotel reception or bank or post office only. Beware of boothes advertising to good to be true rates they are a con. Or to make life easier just take Levs with you.
I just got some Levs in Marks and Spencers today. The exchange rate was 2.796. No idea how this compares to exchanging in the resorts, so I only got a bit for the first night.