How to change Excel column names form A,B,C to 1,2,3 or vice versa

This happens when excel column labels are numeric rather than alphabetic. For example, instead of seeing A, B, and C at the top of your worksheet columns, you see 1, 2, 3, and so on.

The A1 Reference Style

By default, Excel uses the A1 reference style, which refers to columns as letters (A through IV, for a total of 256 columns), and refers to rows as numbers (1 through 65,536). These letters and numbers are called row and column headings.

The R1C1 Reference Style

Excel can also use the R1C1 reference style, in which both the rows and the columns on the worksheet are numbered. The R1C1 reference style is useful if you want to compute row and column positions in macros. In the R1C1 style, Excel indicates the location of a cell with an "R" followed by a row number and a "C" followed by a column number.

To toggle between A1 and R1C1 Reference styles 

1. Start Microsoft Excel.
2. On the Tools menu, click Options.
3. Click the General tab.
4. Under Settings, click to clear the R1C1 reference style check box (upper-left corner), and then click OK.

If you select the R1C1 reference style check box, Excel changes the reference style of both row and column headings, and cell references from the A1 style to the R1C1 style.