If you would like to stay in your rented property after the fixed term of a tenancy agreement has ended you have two choices:
A. Renew your tenancy agreement.
B. Do not review your tenancy agreement and automatically enter into a rolling periodic tenancy if you remain in the property.
If you know you wish to remain in the property for another year, for example, it might be wise to agree a new tenancy agreement with your landlord because (save in certain unique circumstances, listed here) they cannot evict you until the end of a fixed term. Periodic tenancies by contrast are more flexible.