I've had this particular pair of jeans for many, many years, and every summer they come out again - they are beautifully soft after repeated washings, faded to a lovely pale blue, and quite flared with boho-style unfinished hems. Sadly, they have aged better than I have, so when I saw how to reclaim 1" - 2" on the waistband, I was hooked.
Basically, you just remove the too-tight original waistband, and replace it with a folded fabric tie-belt.
I had saved an old king-sized duvet cover from one of my many colour scheme changes, so I just cut a length off one of the long sides. This craftily included the side seam which acted as the top edge, saving me a bit of sewing (you could cut a wider piece of fabric and just fold it, that will work too).
I'm delighted with how this turned out - and it only took about 45 minutes to do from start to finish. So thanks to MeiJo's Joy, I have reclaimed a pair of jeans, just in time for summer.