It is worth noting that a remortgage is not the best option in all cases. Even if the lender you are considering switching to is offering a lower APR, you must take into consideration the facts that:
The new lender may charge you for valuation and solicitors fees, even if you have already paid these for your mortgage with your current lender.
If you switch mortgage remember to look at the overall repayment period. You may be able to pay less monthly, but check the final repayment date of the mortgage as well.