theme won’t allow to get edited

hi! ?? in my previous wordpress interface ( my friend installed it for me ) i was free to edit the theme since there was an UPDATE SITE button.

i just recently bought a domain and hosting, and i installed like 6 themes which were editable. Then voila, the UPDATE SITE button is nowhere to be found. do you have any idea on how i could make that UPDATE SITE button show? im so frustrated. even the Problogger Clean which was allowed to be customised couldnt be edited. help!