Does it have belt tensioners? If yes, just remove old belts and install new ones. The tensioner will move to allow removal and reinstall.
If no, then you'll have to find the accessory that has an adjustable mounting arm (alternator, AC compressor, etc) and loosen the bolt to slide the accessory item inward to release the tension on the belt. Then remove and replace and re-tension the accessory so the belt has about a 1" play in the center.
If you can get to them, it's not a difficult job. However, typically that available room to work is very limited and this makes the job harder.