Need help with tenant

Hello everyone, I need some help regarding a rent increase, we have a tenant in our property. She current has a 12 month fixed term tenancy agreement which ends the 26th May. We are in the process of fitting a new kitchen but we wanted to increase her rent, we have mutually agreed about the increase and signed a document regarding the increase but we are not sure if this is possible during her fixed term. We have read conflicting information on different websites so we dont know where we stand. Can anyone help and shed some light on the situation please? Any information would be grateful. Chris

Duplicate post. Replied on your other one.