Need to change the prefix of schema

Hi ,

I have created new fields in section wizard,however when I tried to change the field code from Usr to my initials.It wouldn't allow me to do it .As,I  don't have system designer section or prefix for schema section where I can change it.I was wondering if there is any workaround to do it.Also,this is studio enterprise demo account.I would appreciate if some one can help me out on this asap.