Keep the sand…good for drainage. You can beef up the soil with compost…we sell composted manure in 1.3 cu. ft. bags (approx. 40 lbs.) that would be prefect for this. Cove the area with 4″ of the compost then blend it into the sand. I’d also add some Espoma Bio-Tone organic food into the soil at the time you’re turning it. This will add organic nutrients as well as beneficial soil microbes to jump start the soil.