First, find out the details of the deal you have at the moment. You may be currently paying your lender's standard variable rate (SVR), which is never likely to be the best deal on offer.
How much is outstanding
Is there a redemption penalty if I repay
If so, how much, and how long does this apply for
What is remaining term
Is it repayment or interest only or both
Check if there is any redemption charge to leave and if so, does this expire at a certain date in future. Even if there is a redemption penalty it may still be worthwhile paying it if the saving in monthly costs is greater than penalty. You Mortgage IQ Advisor will be able to advise you on this.