How do I downgrade my phone version - Software downgrade

[jamaz_73979]

I updated my phone to version 8.0.0 immediately after purchase. Now I want to revert it back to version 7 because the version 8 took up-to 8.5gb of my storage space. It's an infinix hot 6 pro! How do I do it?!
I'm hoping to get back the space the current version took!