@sodhhi
It seems your theme is not yet ready for new version, but it will be soon if theme author makes regular updates.
While that happening, you can change yourself title by a few wp_query functions. To know with one to change, look at code and check query, in general it’s a <h1> or <h2> theme that is called by php and WP functions.
Disabling all themes will lead you to root WP .css and .php functions, sill if not well written by theme it will lead to bad written stuff.
While re-enabling your theme, keep in mind what I wrote behind.
In general, it will lead you to core functions and twenty-etc files.
That often calls “themes-part-files-etc”. The best to be secure, because with WP code security, the best is to call includes this way, so that no external call is possible, but you can include all files in theme folder and other call is wrecked by default – to avoid any hack.
Regards from Paris,