If you have installed the MSSQL Evaluation edition, you can easily upgrade it to the Developer edition. If your Evaluation edition license is expired then you can easily upgrade it to the Developer edition. Please refer to the following steps to upgrade your MSSQL Evaluation edition to the MSSQL Developer edition.

We suggest you take the database backup before proceeding with the below steps. Please refer to MSSQL > Database Backup for more details

1. Download MSSQL Developer Edition from the Microsoft website directly.
   
   
2. Double click on the installer and click on the Run button.
   
   
   
   
3. Once you download with the installer file click to run the setup file.
   
   
4. Click on Maintainance and then click on Edition Upgrade.
   
   
   
   
5. Accept the license agreement and click to Next button.
   
   
   
   
6. Specify the instance for which you want to upgrade the edition and click to Next button.
   
   
   
   
7. Click on the upgrade button.
   
   
   
   

        Looking to check your MSSQL server edition. Please refer to the article MSSQL > Verify Edition for more details.