Open the document containing your thesis on your computer, using Microsoft Word. If you have a different word processor, the method for adding headers may vary a little, but you should be able to find similar options.
Click "View" located at the top of the word processor window, and select "header." A new window will pop up, giving you several options for headers. For academic papers, the plain option is usually the best. Once you have selected a header, the an area of your paper will appear, labeled "Header."
Click inside the header area of your paper and begin typing your information. Refer to the guidelines for your paper's format for instructions on what information to include. If you're not familiar with academic paper guidelines, you can search for them on the Purdue Owl website.
Click "Header and Footer Tools" on the top of the page to bring up a drop down menu. Select "current position" in order to put the page number in your header. You will have several options for the page number. As with the header itself, the plain option is usually best for academic papers.