If you have an active maintenance contract, you can update.
The new license will be automatically downloaded from the license server. If not, you need to download it yourself from the license portal.
That would be all in the upgrade guide you mentioned :)
https://helpcenter.veeam.com/docs/backup/vsphere/upgrade_vbr.html?ver=110
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The Veeam Backup & Replication 11 or 11a setup wizard will offer to download your version 11 or 11a license automatically. This requires uploading your currently installed license to Veeam servers. If your backup server has no Internet connection, or if you prefer not to have your license uploaded, or in case of license upgrade issues – download your license from the Customer Portal manually. Note that you must have an active maintenance agreement at the time when you access the portal.
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