lewaff
The bullets should be in the category.tpl file.
You have a <ul> or <li> or some other "list" tag adding the bullets to your category lists.
Go within the category.tpl and remove or alter it there.
Test this on a test store if possible because I found it difficult to remove the bullet without removing the list, which then puts all the products in one line.
Hopefully that helps
I'm still new at this!