It is not possible to directly convert upper case to lower case letters and lowercase to upper case letter in Excel itself .
It may be possible with help of some macros. But for time being we can follow a shortcut procedure to accomplish the task.
Follow the below procedure to convert lowercase to upper case and vice-versa in MS excel.
1.Copy the row or column of text which you need to convert Small to capital letters or Vice-versa.
2.Now open MS word or MS outlook (HTML view)
3.Paste the data that you copied in MS excel
4.Select All the data by pressing Ctrl+A
5.Now press Shift+F3 , If only first letter is changed to different case, again press Shift+F3 one more time.
6.Now all the selected data will be converted into alternate case.
7.Now select all the data (Ctrl+A) and copy it.
8.Go back to excel, select the first row or column where the data should be entered and Paste the data (Ctrl+V)
9.You can choose Paste with source formatting and formula to get back the same settings as it was initially being set.