Choose the right category to show

Hi guys, I just created a new website with Point Theme (link here)

Unfortunately, I can’t select the right category I want to show on the thumbnails on my homepage (the top left of the small pictures, it’s in blue).

For exemple, a post about some islands in Australia belongs in two categories: Islands and Oceania.

However, it’s always showing the category name which come first in the alphabet (so ‘Island’ shows up instead of ‘Oceania’).

I’ve used different plugin to modify the category permalink but even with that it’s always showing the category which come first in the alphabet…

Basically, I just need a solution so I can display the category I want on that thumbail… I hope you guys get what I mean (english is not my native language so sorry about the spelling mistakes!)

Thanks in Advance, hopefully somebody will help me !