Where you want to change this on Credit Memo, on purchase or on sales CM?
Are you saying you "SEE" this name & when you try to type over it you can't?
Or does this customer have a "Ship-to" code that you want to use?
Or are you saying you want the ship-to to be a totally different customer # like the the "bill-to customer #"?
Is the credit memo "Released" or "Open"?
On a sales CM
If you use Sales Credit Memo, system fills "Ship-to..." fields with information from Location you choose on document header. This name you find, is name of your location. It is normal, because item will be shipped from your customer to your location.
If you don't like this, you can change this data, directly filling in these fields. But again, currently situation is correct.