You can't change feedback you have been left.
You don't have any negatives so I am not sure what you want to change.
Members can choose to make their feedback 'private' so nobody can see individual details or comments.
However, sellers can't have private feedback so, while you have items for sale, your feedback left and received is visible for all to see.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)