Banks in Puerto Pollensa will happily change your pounds sterling and travellers checks into Euro notes. In the summer months most bank in the resort are open from 8.30am to 2pm Mondays – Fridays (except on fiesta days). There are also a wide number of bureau exchange shops in the resort which have longer opening hours than the banks.
It is worth noting that when you cash in you travellers cheques at the bank you will need to take your passport along with you.
There are also lots of cash lines in the resort which you can use your credit and debit card in, which will dispense euros 24 hours per day (it is worth checking with your bank before your leave the UK what they charge for using your card abroad).