Here's how you can change the case of text in an excel spreadsheet:

Microsoft Excel has the following three worksheet functions that you can use to change text case:

LOWER - Converts all uppercase letters in a text string to lowercase.

UPPER - Converts all lowercase letters in a text string to uppercase.

PROPER - Capitalizes the first letter in a text string and any other letters in text that follow any character other than a letter. Converts all other letters to lowercase letters.
By using these functions, you can change the case of existing text in a worksheet. Consider the following example.

Type the following values in a worksheet:
   A1: ABCD
   A2: EFGH
   A3: IJKL
   A4: MNOP
   A5: QRST
   A6: UVWX
   A7: YZ
To make these cells lowercase in Excel 2007 or Excel 2010, follow these steps:  
  1. Type the following formula in cell B1:
    =LOWER(A1)
  2. In column B, select all the cells to the right of the cells that contain data in column A. In this example, highlight cells B1 through B7.
  3. Click Home, click Fill, and then click Down.

    Note The new column now contains the lowercase version of the text in column A.

    Note You can also fill cells B2 through B7 by clicking cell B1, and then dragging the fill handle to cell B7.
  4. Highlight cells B1 through B7, click Home, and then click Copy.
  5. Click cell A1, click Paste, click Paste Special, click Values, and then click OK to paste the converted values back onto column A.
  6. Delete column B. To do this, click Home, click column B, and then clickDelete.
The text that was in column A is now in lowercase:
   A1: abcd
   A2: efgh
   A3: ijkl
   A4: mnop
   A5: qrst
   A6: uvwx
   A7: yz


To make these cells lowercase in Excel 2003 and earlier versions of excel, follow these steps:
  1. Insert a column to the right of column A by selecting column B and clicking Columns on the Insert menu.
  2. Type the following formula in cell B1:
    =LOWER(A1)
  3. In column B, select all the cells to the right of the cells that contain data in column A.
  4. On the Edit menu, point to Fill, and then click Down.

    The new column now contains the lowercase version of the text in column A.
  5. With the same range selected, click Copy on the Edit menu.
  6. Select cell A1, and click Paste Special on the Edit menu. Under Paste, click Values, and click OK to paste the converted values back on top of column A.
  7. Delete column B by selecting the column and clicking Delete on the Edit menu.
The text that was in column A is now in lowercase:
   A1: abcd
   A2: efgh
   A3: ijkl
   A4: mnop
   A5: qrst
   A6: uvwx
   A7: yz


Revised from Microsoft's article "How to change the case of text in Excel":
http://support.microsoft.com/kb/263580