I need to delete and redownload a game on steam, but I'm scared it'll delete my save file

I need to redownload Skyrim, but

1. I'm to sure how to delete is and
2. I don't want it to delete my save files!

How do I this?

First of all, you can backup your game files by following the instructions here.

Then you can right click on Skyrim in the Steam library window, right click and there should be an option to uninstall the game, otherwise known as "Delete Local Content".

Once it is uninstalled you can go ahead and re-install it, then follow the instructions above to take the backup of the save for Skyrim back into your Skyrim game folder. To add your save in, just put the save file you backed up and replace it in the same folder directory as the default one is.

Unless you explicitly disabled the feature in your Skyrim installation. Skyrim game files are backed up to your SteamCloud account every time you exit the game. When you wipe out the game and re-install it Steam will pull your saved game files down from the cloud.