I've replaced the casters on every instrument I bring into the house
using a good quality double rubber wheel ball bearing caster (e.g.
#2592 sold by Schaff).  They are fairly expensive, but they let you
push a piano around the room with one hand, they work on carpets,
and don't mark hardwood floors.

Installation is typically a 5-10 minute task.  I lift one end of the
piano onto a block that allows 3-4 inches of clearance to get the old
one out and new one in.  Pop the old caster out of its socket using
a screwdriver as a lever and pop the new one in.  It would only be
necessary to tip the piano or do something more extensive if the
caster cups were damaged or missing and you needed access to unscrew
them.  It could still be done with the piano propped up a few inches
using an offset screwdriver, but would probably require some patience
and involve some banged elbows and bad language.

It's helpful to have a second person when lifting the piano and
placing the block.  Using a lever dolly makes it easy for one person
to do.  I usually lift using a moving strap under the piano and over my
shoulders so that it can be done using only leg muscles, not risking
back injury.

Cheers,
Roger Wiegand
Wayland, Massachusetts
http://www.carouselorgan.com/