When I changed providers at the end of my fixed rate, I was contacted about a month before it ran out to ensure I had enough time to get every thing done
when your deal comes to an end you normally receive an end of term letter offering you a new rate. you can call your lender approx 3 months prior to this and go through the app and secure the rate thats best for you. alternativley if you want to go through to another lender there are deals out there called switch and save where the new lender will pay you valuation fees and legal fees. a rate switch should not take lond and can be applied in 5 working days. watch out for the application fees they can be hefty hope this helps