Hi Jennifer
You will find a detailed guide to ESA appeals in the members' area
here .
The most important thing to do is to send a GL/24 appeal form within one month of the decision date. If you were claiming Income-Based ESA you can state that you wish to be paid ESA at the assessment rate pending appeal.
Also, if you feel you need somebody to help prepare your appeal you should see the CAB or other welfare rights organization as soon as possible, as they will be very busy at present.
Best of luck
Derek