To change the column names from numbers to letters, follow these steps:

1. Click on the "File" tab at the top left corner of the Excel window.
2. Click on "Options" at the bottom of the left-hand menu.
3. In the Excel Options window, click on "Formulas" in the left-hand menu.
4. Under the "Working with formulas" section, find the option that says "R1C1 reference style" and uncheck the box next to it.
5. Click "OK" to save the changes.

Once you've done this, your columns should be labeled with letters again.

If you want to change the row numbers back to numbers instead of letters, follow these steps:

1. Click on the "File" tab at the top left corner of the Excel window.
2. Click on "Options" at the bottom of the left-hand menu.
3. In the Excel Options window, click on "Advanced" in the left-hand menu.
4. Under the "Display options for this worksheet" section, find the option that says "Show row and column headers" and uncheck the box next to it.
5. Click "OK" to save the changes.

Once you've done this, your rows should be labeled with numbers again.