You can read through the full change notes here.

If you encounter any issues with this update please report them following the process here.

For updates that require a pda update for single player saves, you can run the console command pda readdata to update your save game's PDA. This may sometimes reset all mission progress.
Any updates that require a PDA update will be marked as such in the change notes, though this may not encompass all cases.
This is not needed for dedicated servers as the PDA is automatically updated from the scenario files.

Unless otherwise noted, a new save game is never required for an update. We will try to give advanced notice of any update that would break existing save games but so far RE2 has had no updates that broke save games. If such an update is planned we will make sure you know about it!
Some changes in an update will only show up in a new save game. They will be marked as such in the change notes so you can decide if it's worth it to start over or continue your existing save.
Some changes will apply to an existing save but only in newly generated star systems or playfields.

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No action is needed on your end. Steam will automatically download the update.
However there may be times it does not, in which case you can either verify files in Steam, or unsubscribe then resubscribe to the scenario to force Steam to download the updated files.
For some changes to properly apply to existing save games a PDA update may be required.

You will need to copy the updated scenario files over your existing scenario. Do not change the folder name, simply replace the old version with the new one in the same location.
It's recommended to delete all the old scenario files first to clear out no longer used files.

You will need to manually download the updated version of the scenario from Nexus Mods[www.nexusmods.com] and follow the directions on there to update your scenario.

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Copy the scenario files over to your server again, replacing the old version.
Keep the folder names the same.
It's recommended to delete all the old scenario files first to clear out no longer used files.

You may need to upload your files to a NEW URL and change the URL used in your config to match so clients download the updated SharedData zip. Only applies if you're using the new SharedData download method outlined here:
https://empyriononline.com/threads/v1-11-7-new-shareddata-to-cloud-method.102408/