If you've never used tire spoons, you use one as a lever to pull the tire bead up over the rim, and use the other spoon to hold the tire bead up there, and lever the next section up and over the rim. Sometimes you can tap the lever spoon sideways, to make some progress too.
You work your way around the rim this way, until you have brought the tire bead up over the rim half-way around the wheel. Once you get more than half done, the tire can be more easily wiggled and levered over the rim.
Only do a little at a time, and work methodically.
Try very hard not to bend the rim or chip the chrome.
Some lube can help.
It's not too hard, but it takes some time.
When you re-install, get the tube in nice and flat, and make sure that you don't pinch the tube with the spoons, or get it caught under the tire bead as you are finishing putting on your tire. Otherwise, you'll have a flat tire again when you're finished, and you'll have to do it again to replace the tube you cut.
Check your rim tape or replace it when you have the tire off. If it has wear or holes in it, the spokes can rub a hole in the tube and cause a flat.