Hi Mary,
You need to find the terms with the mortgage, as you can certainly get out of the fixed term by remortgaging, but at what cost? There is usually a early redemption penalty within the fixed term to stop people doing this. It depends on the deal and would usually be a percentage (3%) of the loan. They are sometimes higher than this.
The repayments are high because you only have 10 years left to repay the 77K in loans.
You could look to extend the length of the mortgage, but this would depend on your age, as to when you would stop working and you might have to remortgage to do this.
An alternative is to attempt to switch to an investment mortgage rather than repayment (with your existing lender) where you would look to invest money in an ISA instead of repayment, which sometimes can give you more flexiblilty, but the lender could be strict with this and review it.
You could talk to your lender to see if they would be happy for you to switch to an investment (interest only mortgage + ISA) unlikely given the term, and the amount to save whilst still paying nearly 4500 a year interest.
The 5.75 fixed isn't the best rate when compared to them now, but it's not far off.
Good luck with it
Sparky