To delete your cloud save, you can do this:

Uncheck "enable cloud saves" in the property page - right click the game in your steam library:

Then, you can delete your save file. Steam's cloud save system stores files in a different location from the game install. For me it's here:

C:\Program Files (x86)\Steam\userdata\61138783\509250\remote\PlayerData.dat

Once you do that, run the game, it'll generate a new PlayerData.dat file (fresh save). After that you can re-enable cloud synchronization if you want.