Turn off your iPhone or iPad by holding down the Sleep/Wake (Power) button until the Power switch appears and sliding it to the right.
To restore your device to the stable version of iOS, you'll need a Mac or PC running iTunes and a cable to connect your iPhone or iPad to that computer. Related: How to Reset Your iPhone or iPad, Even if it Won't Boot Device backups created using the beta version of iOS won't restore to the old version of iOS, so you'll need to either restore an old backup or set things up from scratch afterwards.
This process will erase everything on your iPhone or iPad, however. If you're using a beta, or preview, release of iOS on your phone or tablet, downgrading is easy. It's easier to downgrade to the current stable version if you're trying out a beta version of iOS. When a new stable version of iOS comes out, it's usually only possible to downgrade back to the old version for a few days, although there's a trick you can use.
