Edmond - You would need to use the form TR1. Whilst only one partner may be leaving and being replaced by a new one, the change affects whole of the title and so others named on the register also need to be involved in the transaction.
You need to look at the guidance for
transfer of whole of title
The transfer of part relates to situations where part of the actual land in the title is being transferred, for example part of the garden
The fees would be calculated based on the value of the transaction where money is changing hands (
Scale 1) or the value of the property (
Scale 2)
I hope this helps.