Upgrading from Effects Store 1.x to Effects Store 2.x is not supported, due to
the large amount of changes implemented in Effects Store 2.x.

To install Effects Store 2.x when Effects Store 1.x is already installed, you
must first uninstall Effects Store 1.x.  Please see the download of Effects
Store 1.x you have installed for uninstallation instructions.

Also, if you had the Allow Username Changes configuration option (in the phpBB
Admin Panel > General > Configuration page) turned on for use with the username
change privilege in Effects Store 1.x, disable it.  Username changes are now
handled on a page other than the profile edit form.  That option is used by the
profile edit form, but not the other page.