Go talk to your bank - most have financial advisors and often you dont need to book an appointment.
They will tell you the current interest rate, and when that rate may be reduced and so on.
SOME banks may let you transfer an ISA to a different ISA within the same bank, but some may not.
I had a NatWest ISA a few years ago where the interest rate got very low, so I went to see them and asked if I could transfer to a better ISA within NatWest and they said no.
So I went to Santander where I signed up for a 2 Year ISA and they got the money transferred from NatWest.
But my wife had an ISA with Halifax and that was paying low rates, but she went into there a week or so back and they let her transfer it to an ISA still within Halifax.
So when it is time to move it, you need to see if the bank will let you switch ISA within the same company, or if you have to move it to another company.