1. Remove the field from the Layout tab.
  2. Select the field from the Fields list and select Properties.
  3. Change the width to the desired size. X(8) means 8 characters.   So X(25) means 25 characters. You can usually change the field size.  
    • Already entered data will usually stay as entered.   If you want data to conform to the new size, you should re-input the information.
  4. Add the field back to the Layout.
  5. Commit changes.

Important: Increasing field size is always acceptable; decreasing field size can cause issues if the field already contains data that is longer than the new field size.   It is best if you get your field sizes correct before entering data.