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It's far better to do a factory reset and set up your own Google account and apps then.
You should be able to reset from Settings menu as you have it working. You can also reset with the buttons while off via the recovery mode.
Remember to save any media first, and list any apps you will want back on your own account, as it will wipe added data, not the Android system.
Depending on which device you have, this might help, or Google Acer tablet factory reset if you cannot find a setting for it.
http://www.acertabletforum.com/forum/rescue-squad-guides/5168-how-perform-factory-reset.html