Site Acess - make site public dissapeared

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Hi There,

ive finished my website and when i went to site access to make it live and select public, it gives me a line of text saying, im not using simple permissions, what is going on, ive read other blogs about this and juts can work out how to get this back, if i update c5 top newer version will that get me back to default settings again so i can get site live, very frustrating. never turned this to advanced permissions in the first place?

PLEASE HELP :(