if avail the 50g can i download again? i have old version some apps need a ios14

Your tag line says that you have an iPhone 6 Plus. For that iPhone, iOS 12 is the end of the line. You can upgrade to the latest version of iOS 12 (12.5.7), but not to iOS 13 or higher.

As far as storage goes, you need local storage to download apps. The amount of local storage is fixed for the life of the phone. If local storage is full, you might have to delete some things before you can download others.

• The iPhone 6+, released by Apple nine years ago, cannot be updated beyond iOS 12.5.7.
• The extra storage you’re inquiring about is not iPhone storage. It’s iCloud storage.