2015 Macbook HDD (APFS) is formatted as case sensitive. How do I convert to non-case sensitive?

I bought a 2nd hand Macbook a while ago and have only just tried to install photoshop on it. When I do it says that it cannot install on a case sensitive volume and after some research it appears this can be an issue for many different programs.

I've been told that IPartition is usually the best program for this sort of thing but this does not work with SSD or APFS apparently.

Any help would be much appreciated!