You download Lightroom 5.7.1 from Product updates
Then you install LR 5.7.1, and you should be done. All of your photos and all of your presets ought to be there.
It is always a good precaution to make backups of everything (presets, catalog file and photos) on a regular basis, and if you haven't done this recently, you really ought to make these backups before you begin.
Your presets are in the same location for all 5.x versions of lightroom. Nothing to lose.
If you have turned on the option to "store presets with the catalog", you might want to turn that off and let the presets be in their default location so that a later upgrade to 6.x will find the presets to use since 6.x will migrate your 5.x data into a new 6.x catalog.