Hello I have bought more storage and when I go too download any thing it says not enough storage

You need to make room on the phone, the storage you bought is not on the phone.

Managing iCloud storage and what is the difference between device storage and iCloud storage?

You can buy iCloud storage space and move some of your data there. 

Manage your iCloud storage – Apple Support (UK)

and

What’s the difference between device storage and iCloud storage? – Apple Support (UK)