Please refer to screenshot, it should be clear: BEFORE is how it is now, AFTER is how it should be.
I have 2 menu items: BLOG and ATHLETES. These display K2 items and filter correctly the menu items. I have the K2 category module displaying all categories. I need the K2 category module to display only the categories as filtered by the menu item.

Your help will be greatly appreciated. Please help, I have been dealing with this for a while. Website is koolnfit.com. Thank you

The solution could also come from an extension.

Hi. What's the module you are using to display categories? If you are using K2 Tools module then it has an option to filter the categories you want to display by a parent. So in your case you will just need two instances of the module and assign them to these pages.