Root ROM Manager Superuser Denied


My cell phone technical skills are not that strong. I have rooted by Samsung GS3, but have multiple problems.

- Rom Manager and Superuser are getting denied super user access.
- I am getting low storage space warnings
- I am getting low memory warnings
- So I am not able to update apps
- I am not able to view pictures I take or forward them.

This phone is pretty new to me. I had to root the phone so I could teether without having to pay even more while taking care of someone sick. Please help me fix my phone and understand I need 5th grade English in how to do it.

Thank you in advance!