What method was used in the roman empire to choose a new emporer

The people voted for new emporers (and god i hope I'm not wrong cuz if not I'm just gonna sound stupid)

Once emperor and without an obvious heir, he had adopted Augustus. He may have been the first to choose a successor and call it hereditary succession, but he was not the last - Claudius sidelined his own son in favor of Nero, while Nerva "adopted" Trajan to ensure a smooth successio