Which is the correct texture to replace?

After searching google and the forum, I could not find the following information.

I noticed there are two texture locations for the Workspace. One is in the Build folder, the other is in the src folder.

Which is the correct textures to replace?

If you are asking why I wish to know? Well, I have over 100 items now, and I wish to just drop and replace them in batch. At the moment, replacing the ones in the src folder seems to have worked. I'm just worried that it might revert or something.