You won't be able to access encrypted files without the Sookasa app installed, so before you uninstall, please make sure that you've decrypted all the files within Sookasa.
On Mac: From the Applications folder, right-click on Sookasa and choose "Move to Trash." Then, right-click the Trash and select "Empty Trash."
On Windows: Open the Control Panel on your computer and go to Programs. From there, navigate to Programs and Features, select Sookasa, and click "Uninstall."