HI Olivia
Thank you for your enquiry.
This will depend on your lender. Any do allow for up to 10% of the outstanding balance to be paid each year without penalty. This information would be available to you on your mortgage offer when you first applied for the mortgage. You can also contact your lender to find out the limits
If you think it will be over 10% that you wish to pay that it may be worth saving in a high interest account life an ISA and then pay a lump sum at the and of your 2 year fixed. Then your remortgage will be lower.
Many Thanks
Mortgage sorter