You can customize the way Microsoft Office spell checks a document by selecting proofing settings in Options. Some spelling options apply to specific Office programs, such as Check spelling as you type, while other options apply to all Microsoft Office programs, such as Ignore Internet and file addresses, and Flag repeated words. If you have ever mistakenly used their instead of there, you can use contextual spelling to fix it. While you work in a document, you can set options to have the spelling checker search for mistakes in the background.
Click the File tab, and then click Options