MLA manuscript formatting guidelines require documents to be double-spaced, and double-spaced only.

If your Word document contains extra line spacing, the step to correct this problem is relatively simple.

Go to the format setting for paragraphs.  Check the box next to "Don't add space between paragraphs of the same style."  If the document has already been created, you will need to highlight the entire document prior to checking this box. See the image below.