Ankle – range of movement

I have a friend who is worried about his range of movement on both his ankles. He is 56yrs old and is not particularly active. He does not exercise apart from walking to work every day. His ankles do not FEEL stiff and he is not in any pain, but his range of movement is very small and his ankles appear to be swollen slightly. Is there any way of improving his range of movement? Is there specific exercises which would be advisable for ankles which would increse ROM? Thank you for your help people.