I see you are in the UK. In part, what you need to do depends on whether the aircraft is N- reg or G- reg, and on your licence, FAA or European.
For the latter, the rating you need is the Class Rating SET(Land); this extract from LASORs is relevant:
F1.6 REQUIREMENTS FOR THE ADDITION OF A SET (LAND) CLASS RATING
For rating issue you must:-
a. Provide evidence of having completed an approved course of training in accordance with JAR-FCL for the purposes of the rating.
b. Pass a Licensing Skills Test (LST) conducted by a JAR authorised Class Rating Examiner (CRE) or FE.
c. Pass a theoretical knowledge exam (oral as part of the LST).
d. If applicable, meet the requirements of JAR-FCL 1.251 if the aeroplane is a High Performance Aeroplane (HPA). For further details please refer to High Performance Aeroplanes (HPA) within the General Information at the start of Section F.
JAR-FCL1.261/1.262 refers.