how to downgrade to Macsierra?
I have 2015 early Macbook Air and operating Mojave but not pleased with the opening speed .How can I download sierra and downgrade to sierra that I had first MacOS
If you have Time Machine disk, use it to revert to a time before you upgraded to Mojave.
Restore your Mac from a backup - Apple Support
Follow the directions for: Restore both MacOS and your files.
If you do not have TM then you need to erase the disk and install High Sierra. Do a complete backup before this as your data will be erased.
