Capital Gains Tax

I purchased  a detached shop as a sole trader in mid 2000 for £89,000.00. I am now looking to sell it for £170,000.00, hopefully. I have not had any building work done other than internal decoration during my time of ownership. My understanding is I will need to pay capital gains tax on some of the amount over £89,000.00, less my personal allowance. I have two mortgages on two other shops still outstanding at the moment; one for  £91,000.00 and the other for £105,000. Can I use the funds to clear some of these mortgages and will this remove the need to pay capital gains?