Power Gallery does not offer support for unsubscribing without logging in, it requires unsupported custom coding to make this work.
if you want assistance with this, we can help you in a premiere support appointment.
for the upgrade, download the 1.0.2 power messenger zip file.
copy all of the files in the power messenger zip folder over the existing files in the power mesenger folder of your site. Then in the install_messenger folder, copy the install_messenger/webassist folder over the webassist folder at the power mesenger folder of your site