You'll need to establish a level of rent that is both attractive to tenants and covers your own expenditure on the property. When setting rents you should be realistic and remember that letting a property at a slightly reduced rent is more favourable than it sitting vacant on the market.
You are not required to serve a Notice to Quit to bring a fixed term agreement to an end, but you should write to your tenants to find out whether they intend to stay in the property or move on. Finding out your existing tenants' intentions will help minimise the risk of void months, where no rent is paid.
The Rent Officer for Northern Ireland is responsible for setting rents on rent controlled and protected tenancies. If your landlord is charging more than the Rent Officer has allowed, you could be entitled to have this money back.