Under Refine Results on the left side click on View all options
Scroll down until you see Literature Types
Click on the triangle (arrow) next to Literature Types to see your options
Select the Literature Review checkbox, then click Refine
If you don't see the Literature Review option, try clicking "more options/values." Note: Be sure you are searching BIOSIS Previews and not All Databases (or any other Web of Knowledge database). You can check the database you are searching by clicking on the Search button; the database will be shown next to the Search icon.
If there are no literature reviews in your original search results, you won't see a Literature Review option under Literature Types. You may want to broaden your search, then try limiting to literature reviews again.