You can increase you fitness by doing 10 mins of brisk walking 3 or 4 times a week. Brisk means you can talk but not sing whilst walking, increase your distance on each attempt .
Stand up then sit down ten times without using your arms, reducing your time on each attempt.
Four times a week: 6 minute mini gym workout:
Gentle jogging for 1 minute
Star jumps for 1 minute
Squats for 1 minute
Static sprinting for 1 minute
Star jumps for 1 minute
Gentle jogging for 1 minute
Increase your arm strength using a lightweight simply lift it until you cannot do the lift any more, ensure correct technique and posture is adopted.