A replaced knee likes movement. Walking, cycling, swimming and similar low-impact activity are excellent for it - and for you - for the years ahead.
Keep some strength work in your week even after the program ends: strong thigh and hip muscles protect the joint and keep stairs, chairs and hills easy.
High-impact sport (running, jumping, contact sport) is a conversation to have with your clinician - advice differs from person to person.
Keeping a healthy body weight is one of the most effective things you can do for the comfort and lifespan of the new joint.