The simple solution is to tip the piano onto its back.  First, move
the piano away from the wall by about 8 feet.  Then, place two pieces
of wood, say 3" x 2" x 8" long, onto the floor behind the piano.
Position them so they will end up about 6" inside the width of the
piano when down, and sticking out from the back of the piano by a few
inches.  Then, two or possibly three people position themselves at
the rear of the piano, and slowly lower it down onto the blocks.

The purpose of the wood blocks is to enable one to insert ones hand
under the piano to lift it upright when the job has been done.  I can
vouch for this method as I've used it countless times over the years,
to work on piano castors.  It doesn't require any fancy equipment,
except the two blocks of wood as mentioned.

Regarding suitable replacement castor, the best sort to use are
Rubber-tyred castors, bought from a piano supply house.  These are
made to withstand the weight of the piano.  They are fairly expensive
but well worth the expense, as they move beautifully and will not
mark wood floors.  Hope this helps.

Steve Toyne