Thank you for the link, although I'm not sure on what to do... I'm not very "high tech" and it seems like you have to be to get everything.
I know that I haven't upgraded my themes to the latest version but I'm afraid of doing so since my whole site is customized and above the "update" button it says: "Any customizations you have made to theme files will be lost". Can I updated them even though my site is customised?
That's the only thing I got from the link that I haven't done...