Update:
There is unexpected issue with the update of this template specific so you can't update via JA Extensions manager at this moment.
We suggest you to backup your site, then download the latest version of this template: https://www.joomlart.com/member/downloads/joomlart/t3-framework/t3-blank
and install directly to your site.
Next time, you will be able to update via JA Extensions manager.
Again, remember to backup your site first.
We're sorry for any inconvenience it may cause.