Urgent Help Required regarding visit visa

HI to all

i have applied for canadian single entry visit visa and i have been granted that visa on the grounds that i am going to canada to visit my friend for her medical treatment,,

but now i want it to be changed to multiple entry visa,,can some please advise me how can i do that,,i will be getting my passport on 8 june and i am planing to travel on 10 till 21,,but i again want to travel to canada on 3 july,,so should i apply again for visa after coming back on is there something that can be done untilll me passport is with them,,,

i am a student here in london,and have applied in canada embassy london




please guide me everyone ,,i shall be very thankfull to you all..

Best thing to do is to apply again when you come back