Advice on buy to let mortgage from 2004

hildamay1

We applied for a mortgage in 2004 for £50,000 over 10 years.This was for a garden room in our own house on which we owed no money. We were advised by Nat West that the best and easiest way to borrow the money was with a buy to let mortgage as we also own a couple of properties that have no mortgage. We have to pay 62 payments at a fixed rate of 5.95% (£553.85) until 31/1/10 and then 58 payments at a variable rate (Which was 7.29% at the time of taking out the mortgage) - £582.21
We feel now that we have paid far too much for this mortgage and hope to reduce the payments somehow. Any advice please