Safe moving
My brother moves safes for a living.
As far as your situation: go buy 2-3 pieces of plywood (scafold planks work best but are kinda heavy) & rent a appliance dolly (the kind w/ a strap). Get a couple of friends to pick up & move the last pc. of plywood & make a ramp down to the house. Pick it up... set it down... pick it up... make sure you don't hit/cross the joint in the ramp w/ both wheels of the dolly @ the same time or you'll sink into the grass. Roll 1 wheel & then the other. You can lay a thin sheet of sheetmetal over the joints also.
I wouldn't suggest doing the move while the grass is wet for fear of slipping.
If you ever have to move it inside the house, we use a furniture dolly or golf balls. Be carfull using golf ball on hardwood floors.
Hope this helps.
edit: Don't forget.... guys doing it for a living have experiance & tools. Don't do the move yourself trying to save a few bucks. Grymster2007 is right! Even the "Pro's" can loose a 1500lb safe during a move!
We call'em "Bulldoziers" for a reason.