Your model came with a special version of Snow Leopard on DVDs. To install anything above that version requires you install Lion. You can install Lion without having to first install Snow Leopard. Either have your recovery DVDs available or install Lion.
You can purchase Lion at the Online Apple Store. The cost is $19.99 (as it was before) plus tax. It's a download. You will get an email containing a redemption code that you then use at the Mac App Store to download Lion. Save a copy of that installer to your Downloads folder because the installer deletes itself at the end of the installation.
Are my applications compatible? See App Compatibility Table - RoaringApps.
To install Snow Leopard from your DVDs:
Snow Leopard Erase and Install
If possible be sure to back up your files.
- Insert Snow Leopard DVD into the optical drive and restart the computer.
- Immediately upon hearing the chime hold down the C key.
- Release the key when the Apple logo appears and wait for the loading to finish.
- After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities' menu. After Disk Utility loads select the out-dented disk entry from the side list (mfgr.'s ID and drive size.) Click on the Partition tab in the Disk Utility’s right window. Set the number of partitions to one (1) from the drop down menu. Click on the Options button and select GUID, click OK button, set the format type to MacOS Extended, Journaled. Finally, click on the Apply button.
- After formatting has finished quit Disk Utility. Continue with the OS X installation and follow the directions.
- When the installation has finished the computer will restart into the Setup Assistant. After you complete the Setup Assistant you will be running a fresh installation of Snow Leopard. Open Software Update and install the recommended updates.
- Download and install Mac OS X 10.6.8 Update Combo v1.1.
- Go to the App Store for further upgrading. See How to download macOS High Sierra to find out what you must first install in order to upgrade to High Sierra.