Microsoft Excel keeping all cells uppercase

You can use another way, it's forcing users from the beginning to enter uppercase characters through Data Validation feature.

Just follow these steps:

• Select the entire column you want.
• Go to Data Ribbon Tab >> Data Tools Group >> Data Validation

• From Data Validation dialog box, select custom from Allow combo box.
• In the formula bar copy and paste this formula:

=EXACT(A1,UPPER(A1))

• Press OK.

After that, users are not allowed to enter lowercase characters in column A.

NOTE: If you want to apply this to a column other than column A, select that column entirely, and change the cell references in data validation formula.