Dear Button,
Just be brutal! cutting down any work is always difficult, you just need to identify the major works and ask yourself 'does the reader need to know this'. There are a few techniques that may help. For example, you could try grouping authors/literature together into clear schools of thought and write about the more broader developments in the field rather than specific studies. You could also be a little clever with the referencing. Depending on what referencing style you use and your discipline, you can use footnotes or endnotes, for example, to signal to the reader that you are aware of the more obscure literature etc. - but, obviously, don't overdo it.
Hope that helps, and good luck
Best,
Si