If you do not wish to change character encoding for the entire server, but only one site (or only one directory) then this is possible to do using .htaccess.

AddDefaultCharset UTF-8

If you only wish to do this to php or htm files (and not all files)

<FilesMatch "\.(htm|php)$">
AddDefaultCharset UTF-8
</FilesMatch>

If you wish to modify the mime-type as well as the encoding (on html files in this example)

AddType 'text/html; charset=UTF-8' html