Original Post — Direct link
So, I have the standard edition of the game, and I want to upgrade it to Deluxe edition. Unfortunely, I can't. I submitted a ticket about it on Steam, they gave me this answer.
How can I purchase Deluxe edition without paying what I got again?

Here's the answer Steam Support gave me:

Please do know, we do not offer package upgrade, exchange or refund the difference for any games purchased on Steam.
Unfortunately, since you already own the Deluxe version of the game you can no longer purchase the Operator edition.
The only way to purchase the Operator edition is to refund your initial purchase. But, your purchase does not qualify for a refund.
I highly recommend to contact the support team of the game, and ask them if they can provide a possible upgrade option.
over 3 years ago - Ubi-Raziel - Direct link
Hello, I hope you are well!

We do not currently have the option to upgrade between Rainbow Six Siege editions. If you wish to access a larger edition, that edition would then need to be purchased.

If Steam would be willing, I believe the only option would be for the game to be removed from your Steam account so you can then purchase the correct edition.

With all of that in mind however, the Deluxe Edition Year 1 & Year 2 operators, all of which can instead be purchased with the in-game operator bundles for R6 Credits.

You mentioned you're unable to buy DLCs. Can you please elaborate on what is happening?

Thank you!