There are two topics about this and it’s not possible.
If you haven’t already, I suggest you do a quick search when you look for basic information, they might have already been answered in the past 
Jay has a point tho:
Allowing some users to upload files while others cannot may inconvenience both users and admins. External links are unreliable by nature, likely to expire in the future, or worse, be automatically replaced with something else. That has happened on one of my forums.