When you refer to chapters and first level subheadings of your manuscript within the paper itself, capitalize the first letter of each word. For example, you would write Literature Review, rather than literature review. The reasoning behind this rule is that because these are titles, they should be treated as proper nouns. A good rule of thumb to follow is that if something is in the Table of Contents, it needs to be capitalized.
However, be careful of wording similar to chapter and section titles, such as: "The literature reviewed in this chapter . . ." The 'l' and 'r' are not capitalized here, as you are referring to literature that was reviewed, not to the Literature Review chapter of your manuscript.