How do I set microsoft word 2010 back to it's defult settings?

You need to delete the normal.dotm template. This is the blank template that Word uses when it opens a new document. If the settings on it have been changed, then just delete this template and the next time you open Word it will have the default settings again.

Make sure Word is closed.

It's location is:

C:>users>[your name]>AppData>Roaming
>Microsoft>Templates

You will see normal.dotm. Click once on it to highlight, then delete.

Now reopen Word and the settings are back to default.

NOTE: this is a hidden system file. You will need to set your folder settings so that you can View hidden files else you will not see the AppData folder. To do that:
Control Panel>Appearance and Personalization>Folder Options>View>Show Hidden Files, Folders and Drives.