Help with making liveries

Hi. I’m new to all this and need some help.
I know about making textures and the like but im unsure on how to handle things like decals.
I’m looking at the Cessna 152 specifically at the moment and it has a texture for decals as do a lot of aircraft.
Is there any way to remove this so i can just paint on the base for simplicity?

Another thing is that i can’t find the textures for liveries other than the default in the official packages for some reason, but they work perfectly fine in game so im not sure whats up there.

Here is a good video to start with.

Its on the old side but teaches you the fundamentals.