XF 2.0 Custom title with html in admin panel


Hello! How and where can to modify to accept add html in custom title, only through admin panel forum ? I mention that in another platform (invision power) I succeeded by modifying the file members.php from FTP.
And where I can modify length value to custom title from 64 to 255 characters? I do not find the members table in the database.
Thank in advance!