If you compare rates and find that you could be getting a better deal elsewhere, then do a cash ISA transfer. It's possible to make cash ISA transfers at any time, into another cash ISA or into a stocks and shares ISA, but it is not possible to transfer from a stocks and shares ISA into a cash ISA.
Be aware that cash ISA transfers have to be done through the new provider and they will carry out the process for you. If you just withdraw the funds from your cash ISA with the intention of putting them into a different one, this will count towards your total ISA allowance for that year. Or, if you have already deposited up to your total allowance, you will not be able to pay the money into another ISA until the next tax year. Cash ISA transfers done through the proper process will not count towards your ISA allowance.
Compare deals and make a cash ISA transfer to make your money work as hard as possible – keep an eye on your interest rate and if it falls, consider switching. Or if it's a fixed rate, make sure you shop around when the deal comes to an end.