Change willingness is in terms of the college selection and related to the specific branch which was chosen earlier in the previous rounds of counselling.
If at all you wish to change your option to get admission in a particular college we say it is change willingness to join that particular college.
If the meaning is not clear yet do let me know in the comment section.

Hello Shefali,

Change willingness meaning in general term is to change accorging to our will. Also we can say that change at our option.
You have to specify that in which consent you are asking.
Hope you hear from me.