You can block a user by following these steps;
- Go to the profile of the user you want to block
- Click on the three dots on the right hand side of their profile
3. Click Block
This will stop the user from being able to comment on your uploads. If you'd like to stop notifications of uploads from that user then you'll need to edit your notification settings instead.
NB to unblock a user, follow the steps above and click 'Unblock'