I'm working on someones page and im just updating it. Now the page is very old and is using old html 4 coding.
You don't need to update anything. HTML 4.01 is not old. HTML 4.01 strict Doctype and coding are as good as XHTML Doctype and coding. XHTML is not the new version of HTML 4.01, it is just a HTML 4.01 adapted to handle XML objects, codes and files. The new version of HTML would be HTML 5, but this is not yet (or incomplete) implemented in all the browsers. HTML 5 will make HTML/XHTML Doctypes useless, as the coder will be able to use either HTML style coding or XHTML style coding on his will.
Regarding the charset. It is true that UTF-8 is recommended instead of latin 1 (ISO-8859-1), but if your pages were written in ISO-8859-1, changing the special characters in order to fit the UTF-8 would be an awfully find/replace job. ISO-8859-1 remains still a valid charset, thus I don't think you need to change it by all means.
Post a link to that site, and I will tell you how old is your code and what you might need to make it up-to-date.