ossi2612 Hi
Kindly ensure if you have setup JA Extension manager as per steps outlined here
From back-end, go to: Components → JA Extension Manager then select Service Manager, now set JoomlArt as your default service. Next, hit the "Edit" button then add your Username and Password that you signed up in JoomlArt.com.
But it doesn't work with the Joomla-Installer (path does not exist)
You may also try to install latest template version following other ways to install as outlined here
Upgrade Method:
You can install new version directly over this version. Uninstallation is not required.
Would suggest to also take backup of your site before performing aforesaid steps, in case rollback required whilst facing any issues e.t.c
