A family of Microsoft word processing software products for creating web, email, and print documents.
Are you saying that the Word window is small or that the Word document is small in the Word window?
If the window is small, either maximize it (using the button in the upper right corner) or make it larger by dragging on a bottom corner.
If the document is small, increase the Zoom by dragging the slider on the status bar. The fact that the document is in a corner suggests that you may have multiple pages displayed; if the document were just a single page, it would take up just part of the window.