There should be a pull up bar in your local gym. Jump up and take hold of the bar and make sure your holding the bar right at the end (where the bar bends) and pull yourself up, if you can’t pull yourself up then you need to use the pull up machine where there is a seat for your knees.
1st set 10 reps
2nd set you may add a small weight around your waist like 2.5 kg or do 8 reps
3rd set 8 reps
4th set 6 reps[image from bodytrainer.tv]