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.
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