The Corner Ad has square form, so it is recommended to use proportional images.
Yes, the Corner Ad was implemented with SVG and HTML. So, it is supported by all modern browsers, even the mobiles versions.
The "Corner Ad" is supported by all browsers with Flash player installed.
Note: If you have Flash Player installed but the Corner Ad is not showing, then check if exists any browser's extension that is blocking the Ads.
Note: The above is a safe process, the plugin's data and settings won't be lost during the process and will appear again after installed the pro version.
Alternative Installation Method:
The upgrade instructions are exactly the same instructions mentioned above but be sure to make a backup copy of your current files if you have made custom modifications to the files or translations since the files will be overwritten.
After upgrading the plugin remember to clear your browser cache.
The free version must be deleted before installing the pro version.
If you are upgrading the pro version to a new version you should also remove the previously installed version.
This is a safe step, the plugin's data and settings won't be lost during the process.
Another alternative is to overwrite the plugin files through a FTP connection. This is also a safe step.