1, luckily it wasn't necessary for jim to take the exam again(need)
=> 1, Luckily Jim didn't need to re-take the exam.
2,although he is intelligent,he doesn't do well at school(despite)
=> 2, Despite being intelligent, he doesn’t do well at school.
3,we didn't go to the theatre . we stayed at home(instead of)
=> 3, We stayed at home instead of going to the theatre.
4,we must replace the loudspeakers . the current ones aren't satisfactory(since)
=> 4, We must replace the loudspeakers since the current ones aren’t satisfactory.