I have not so far mentioned page layout. Here, Word’s default layout is fine. I suggest you keep it and set all your text to 10–12 point single line spacing. You can change settings if you like, but examiners know all the tricks. Setting your dissertation 16 point triple-line spaced with 2.5 inch margins all round will certainly make your dissertation look thicker and may impress your friends, but it will not impress the examiners one jot.
You may want to copy in diagrams, figures or tables created elsewhere (e.g. from Excel or SPSS or a website). Word’s copy and paste facilities are very good for this, but watch out. Word has a feature (some would say bug) that can make life difficult. If you just paste a picture, it gets "floated over the text". In practice this means it can float just about anywhere. The way to get around this is always to use paste special and make sure the "float over text" box is unticked.
One final comment: for technical reasons no Microsoft product was used in the production of this document; so if you are reading it as a Word document, it is probably not formatted as it advises. Nonetheless, similar formatting instructions were used to generate the document.