If you really want to make sure you 810 has the newest firmware, install and run the Windows Phone Recovery Tool. It will download the "Official" firmware and OS (it's really Amber and W8.0).
Be forewarned... IT WILL DO A RESET AND WIPE OUT ALL DATA ON YOUR PHONE. Make sure you remove any microSD card you have inside and make sure you have a good backup on OneDrive or copy off any photos, music, docs, etc. manually before running the WPRT.
Then I recommend that after it's done do the following:
Use you MS account.
Do NOT choose a restore.
Install the Developer Preview and set it up.
Check for updates.
It takes 3 or 4 updates to bring the phone to W8.1u2
Then reset the phone again (Settings, about, reset your phone).
Use your MS account.
This time restore from backup.
Turn off Auto update apps as soon as you can.
Check for updates, and install them if needed.
Then turn on auto update apps.
Update your apps.
I know this is a lot of steps, but since the 810 became the red headed stepchild of the Lumia's, this is what we have to do