Typically fixed rate mortgages remain fixed for the entire term
If you have a fixed-rate mortgage, the interest rate is fixed for the entire term of the mortgage.
You should be aware that it is quite difficult to change mortgages in Spain. It’s nearly impossible to switch from a fixed interest product to a variable rate one and vice versa once the mortgage has been granted.
There are mixed rate mortgages that start at a fixed rate and then switch to a variable interest rate at a defined point in the future, but this is contractually pre-agreed. You should take great care should you consider this as an option due to current low-interest rates and the risk of paying considerably higher repayments after the initial fixed term.