I already help you updated latest version of Easyblog on your site, can you give it a check?

By the way, that is not possible to upgrade through Joomla updater is because Easyblog 5.1.15 version still not updated the latest launcher file yet, but this will possible when you update from Easyblog 5.2.1 to next release version in the future.

Thank you very much for your speedy and adequate reply!

You are most welcome sir and I do apologize for the inconveniences caused as the single click updater is something new we introduced in 5.2.1 and we needed to iron out some issues with the single click updater script.