Best thing to do is to make a copy of the site on a development system, then you can experiment with whatever updates you want without risking your live site. Use that to gather experience, work out what will and will not update, then (after making a new backup) apply what you have learned to updating the live site.

A safer variation of the last stage of the above is to then clone the live site into a temporary domain (maybe a subdomain), update the clone, check the clone is ok, then point the domain name at the clone.

Its also usually safest to change a site to a default theme during update, so that any theme update issues do not lock you out of the site.

Good sound advice. Thanks. I have development testing and live environments so i Should probably use them and stop being lazy.