Welcome @Zeki_Mustafa. You cannot change an imported playlist, you must first save a local copy. Once you have done that you can delete, add, sort, filter and so on.
The Roon Knowledge Base article on playlists will give you all the information you need.
For the default view, you need to configure the Now playing screen. You can change the order they come up via in the screen menu option from the three dots on the now playing screen.
Here’s a very useful post which explains things better.