Around Morelia on the Periferico!
As you approach Morelia, turn right at the Periferico. It's a multi-lane loop with lots of traffic and stop lights. Either direction can exit at the Patzcuaro highway but right is easier.
Arriving from the north, either the airport or cuota (toll road) from Mexico City/Guadalajara, you'll approach the ring-road on an overpass bridge. Signage for the right hand exit says Patzcuaro.
Go half-way around Morelia and take the next exit past Quiroga exit towards Patzcuaro.
As you approach Morelia from the south, Patzcuaro or Uruapan, turn right on the Periferico, towards Mexico City/Guadalajara. Go half-way around and exit at road to Mexico City/Guadalajara.