its really simply. dont be afraid your gonna bend the top door off it takes alot of force to slightly bend the door frame! and if you bend it alittle to far its no big deal after the door open and closing a few times the door will bent itself back alittle.
when i had my truck you REALLY had to put your back into it yanking that top door frame towards your chest hard for it to move. but i was a full size truck so nice and beefy.

best thing to do is try it alittle and check. simply close the door and look at how the top door frame looks on the top of the car if its sticks out alittle like it does now try it again with alittle more force and retest it again.
very simple.

put your hands thru the open window frame and grip the top frame of the door and pull the frame towards your chest.

 

lol funny pic

 

LOL its just that simple!
tho dont brace door panel because it might break. put your knee on the metal frame, and just pull

 

LOL not really. just showing what ya need to do. i didnt have to bent my door frame. mine seals fine
but that is what i did on my old truck wth alot more force!

 

no leak over here.