heat nozzle - remove old filament.
insert new filament
ta da !
New filament :-)

If you want to change filament mid-print. there is probably a pause print option on the printer control panel.

I've never done that.

I've occasionally poked new filament into the extruder directly behind a run out reel. That works pretty well.
Well as long as the print doesn't have a bunch of retractions.
Because while a new piece of filament can push the old bit along the tube, it can't pull it back for a retraction.

So there's that.

But just a filament changeover, takes about 5 minutes.