MS Word settings not sure which MS Word I’m using?

My teacher sent me this email and I don’t know how to do what she’s asking me to do? I’m using MS Word and i know its set up wrong but don’t know how to change the setting: Please set up your word-processor for a letter-sized document. Your past two assignments have been set up as legal-sized documents???? how do i do that please?
There are a few different document sizes in MS Word to choose from and if you have the wrong one it can drastically change to look of your document. When printing it out you will notice an even bigger difference. You can choose from Letter size, Legal, Executive, A4, Various envelope sizes, and more.
document sizes in MS word

Microsoft word 2007 – Change Page layout to letter size:

  1. In Micorsoft Word 2007 go to the Page layout tab.
  2. Choose size from the Page setup section.
  3. A drop down menu will appear. Choose the document size you want.
See the screen shot below.
letter size documents in word

Older versions of Microsoft Word

  1. Go to the file menu at the top of the screen.
  2. Choose Page Setup from the drop down menu.
  3. When the Page Setup dialog box appears, click on the paper tab.