Termination of Gaurdianship

My mom has guardianship of my children in California I reside in Tennessee. it is stated in a letter from her to the courts saying that she was to be their Guardian only until I got "back on my feet". but now i am in fear of her carrying out this guardianship for as long as she can with no intention of agreeing to terminate it consensually. however there are no conditions listed as to what I need to do to prove that the children should be with me. I was verbally given some expectations one time over the phone. I have nothing in writing...no check list or anything to refer to ensure i am on the right path... there is obviously a story to unfold here for anyone willing to guide me and answer some of my questions please let me know. With that, I will go into more detail giving everyone an understanding of the events that lead to this ..what im up against,etc. I am spinning in circles and I need to move forward instead of nowhere thank you for your time.