Replace Water Heater DIY?

[Jon Dang]

I recently bought a quadplex and my insurance company requires me to replace all 4 water heater (15 yr+ require replacement, standard in my area). I found some 40 gallon at home depot for about $350 each. 

I got quote to replace water heater at $500-1000. I am considering replacing them my self. I live/househack one and another unit is vacant. I might hire out the two with tenants. But, how hard is it to repace a water heater? Any advice? I am looking at an electric water heater, closet heater, first floor.

I only owned this place for a month now and I'm trying to save while I build reserves.