Click "Save." Overwrite the original file. Launch Castle Crashers via Steam. Your changes should be live in the character select screen.
Since the cc_save.dat file is encrypted and tied to your specific Steam ID, simply downloading a "100% complete" save from someone else often won't work. Instead, you can use these tools to modify your own file: castle crashers save editor steam
While Behemoth (the developers) is generally relaxed about save editing for personal use, Some players prefer a "clean" game, and using an "over-leveled" character can ruin the challenge for others. Click "Save
Open the editor. Click "Load" or "Open Save." Navigate to the .sav file you found in Step 1. Some players prefer a "clean" game