You can replace ungrounded receptacles with a grounded ones.

In some cases it is easy, other more harder.

1. If the existing wiring system uses Armoured Cable, AC (commonly refered to as BX cable) or use ENT conduit then you connect a ground wire to the metal box and to the receptacle.

2. You can run a separate ground wire that connects back either directly or indirectly (to another box with a ground wire) that connects back to a part of the ground electrode system including the electrical panel. This is an exception to the common run that wries can only be part of a cable or run in conduit.

3. Run a new grounded circuit.

4. Use a GFCI receptacle or have the receptacle protected by an upstread GFCI or GFCI breaker. In that case the receptacles are to labeled NO EQUIPMENT GROUND. Individual GFCI’s come with those stickers.

The latter method gives full personal safety, but does not provide a ground for things like surge protectors and electronic equipment.

Also things like a refigerator, freezer, or sump pump should be on a true grounded circuit and not a GFCI because of the losses from a false trip.