Well, there are a lot of dangerous ways, but the only really safe way is to support the door with a padded jack, remove the lower hinge, replace the spring safely with the hinge in a vise, and put the hinge back on. Little or no adjustment will be needed if you mark the position first.
What i've found that works even better is to use an engine hoist with a padded strap looped under the door. This way you can giggle and move the door a little without worrying about it falling down.