Ok the hinges are screwed to the door and bolted to the the A post via studs on the hinges. If you have a look in each front wheel arch and look back you will see two sets of nuts. These are the hinge mounts and these are what you can adjust, not the screws that hold the hinges on to the door.
If you decide to go this route you must soak these nuts with GT85 or WD40 as the studs on the hinges have a habit of shearing but if the garage has re skinned the doors then they should be ok but do spray them anyway.
Its best to have two people to do this job also put some masking tape on the edge of the door and A panel to protect your paint. Make yourself a couple of reasonably strong plastic shims or levers to put along the bottom of the door and door step to enable you to keep the door level when you go to re fit it. Again put masking tape along the door edge to protect the paint.
The door is not too heavy but be careful. There may be shims under the hinges where it meets the A post, do not lose them and do not forget to fit them.
Have a play around with the door to see if you can tighten the gaps, if there is not enough play in the A post holes then open them up a little bit DO NOT GO MAD.
Its really down to you on this bit as to have far you want to go with the adjustment. Just be careful and be patient.
To give you an idea this is what i used to do the doors on Project Erm
Hinge assembly

The two studs you can see with the shim are what you can adjust on the A post
Hope this helps