Hi Monika,
You can have desired column heading by following 3 ways.
1. Change to a standard data element that has the description Customer and Employee. This might not be as simple as you have to find one with data type that is usefull to you.
2. Change the column headings on the dynpro screen generated as mentioned above by D. Floor. This is not a sustainable solution though and will not recommend unless you weigh this option better that 1. and 3.
3. Copy the standard data elements that you think work best for you to Z. Change the Description and Label to match best with your application.
Regards
Sachin