Speak to the mortgage lender and ask if they can remortgage in your sole name or speak to other mortgage lenders to see if they can do the same.
Depending on whether your brother is a registered owner and what contributions he has made to the property there may be financial issues.
You may need to take him off the property register if he is on it to allow a remortgage as lenders don't tend to like anyone not on the mortgage being on the title due to their interest in the property.