Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Do you mean that you would like to upgrade Microsoft 365 E3 to Microsoft 365 E5?
If so, the easiest way to do this is to use the Upgrade tab in the admin center. However, using the Upgrade tab isn't supported in all situations. In some cases, you might be able to change plans manually.
For detailed steps, you could refer to “Upgrade to a different plan” and “Change plans manually”.
If you have any questions when upgrading, please Call Microsoft support.
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