Url is constructed from menu structure, so one of the parent elements has to has "about-joomla" as alias. "kategori" and ID must be coming from advanced K2 sef settings. You can change it in K2 > Parameters > Advanced > Advanced SEF Settings.
If it's regular joomla articles than it should be handled by SEO options in Global Joomla Configuration. For sure You will need to create a separate menu item for each category to replace "kategori" with an alias, but I'm not sure how to get rid of ID, sorry (none of my installations is showind ID, so I have nothing to compare it with). Try asking this question on joomla forum.