PhpStorm/WebStorm cache folders

I found the following folders in the library cache directory on my MacBook pro:

~/Library/Caches/PhpStorm2016.3

~/Library/Caches/PhpStorm2017.1

~/Library/Caches/WebStorm2016.3

~/Library/Caches/WebStorm2017.1

Each of them takes 500Mb~1.1Gb in the system. 

The laptop has a smaller flash hard drive. Is it OK to remove the 2016 ones and just keep the 2017 ones?

Is there any special reason they are kept separately in the system? Just wondering why they weren't removed / replaced when a newer update was installed?

Thanks.

Lu