Can't find Theme inside the package folder to install in 5.5.11 user found helpful
- the theme is there
- it is in the right place
- that it has a package controller, so can install correctly
Also, did you download it from Concrete5.org, or from another site? If from another site, is the theme compatible with Concrete5?
My theory is that the directory structure is incorrect, and thus concrete5 is not seeing the package.
Normal installation would be something like /packages/cooltheme/themes/cooltheme
Sometimes when you download and extract a package, it creates an 'extra' top level folder. If you upload that to /packages, you'd end up with a structure like /packages/cooltheme/cooltheme/themes/cooltheme which will not work.
It should be something like