Step 1: Click on the field for which you want to change the description.
Step 2: Click on F1 and then on F9.Take a note of the data element.
Step 3: Now go to transaction CMOD
Step 4: Click on Goto -> Text enhancements -> Keywords ->Change
Step 5: Enter the data element and click on V
Step 5: Enter the desired label/description for the field and save it.
Now your field description is changed to "Exp.Revenu" (in this case). The change gets reflected to the Web UI as well.There is a way to perform the same task using UI work bench. I will post it up on my next post.