Gallery2 upgrade says that g2data folder is unwritable and its permissions should be set to 777When you get this error message, you have to login to your cPanel, then use the File Manager to change g2data's permissions.
When you browse to this directory using the File Manager, you have to click on its name and choose Change Permissions from the top menu.
Once g2data's directory is writable, you may proceed with your Gallery2 upgrade.