Update 18.5.1 MR-1 is not displayed

Sophos use "Staged rollout" for upgrades.
Possible you got the Firmware next days.
Another option is to go to sophos-central and download the available firmware for your device.

https://community.sophos.com/sophos-xg-firewall/b/blog/posts/sophos-firewall-v18-5-mr1-is-now-available ... 

goto "How to get it"

Okay thank you!

We using this KB to update the firmware manually. We can download firmware and upload this firmware to our Firewall but at the end of the upload the message "The firmware will boot the device with factory default configuration. Are you sure you want to continue?" . Our problem is that we do not want to reset the device to factory default settings but only to update to version 18.5.1.

You have an idea to fix this issue?

V18.0 MR6 does not support a upgrade to V18.5 MR1. 

So you have to wait until V18.5 MR2 will be released (Soon). This will cover the upgrade path. 

IS there any update on this yet ? IE the release date