Debtors records are maintained via the DB Debtor Maintenance form. This can be accessed from the Financials menu by selecting Debtors > DB Account Maintenance > DB Debtor Maintenance:

In this form you can add the Debtor number to the Debtor Number field and then selecting the
button located at the bottom of the form will open the Debtor's record:

Alternatively you can use the search facility to find the relevant Debtor. Click on the Find Debtor button located to the right of the Debtor Number field,
. This will open a DB Find Debtor form:

The DB Find Debtor form is further detailed in the Debtor Enquiry section.
Once the Creditor record is open you can make a range of changes. There are further detailed in the Amending Debtor section.