How are you planning to stretch it? Is it just too snug? Or do you want to change the crown height and brim width?
You can stretch the hat to fit and use steam and gentle (little at a time) turn of the handle on the hat stretcher. Get one of the good vintage ones that are on ebay all the time.
If you want to redo the entire hat, I'd sent it out to have it professionally done. Remember, the sweatband needs to be replaced if it becomes too short, the lining must come out or you will iron seam patterns thru the felt, and lastly, the felt comes from somewhere: if you raise the crown the brim will become narrower.
If this is a 1983 hat, it may not be the best quality felt.