If you are living in Portugal and are resident and still have not changed your UK licence to a Portuguese one, then this needs to be done before the end of this month.
If you are planning to move to Portugal and become resident after December 31st then you have 90 days from residency to change this.
This is a screen shot from the UK GOV website.
You can change your licence in Funchal at this address. R. do Seminário n.º 21, 022, 9050-022 Funchal
You will need a doctors certificate to show you are fit to drive, this can be from a private clinic and will cost about 19 euros, plus the usual paperwork, NIF, residency, old licence. The cost to change is 35.00 euros I believe.