They have the usual transport options: shove into cargo area, on a flatbed truck, shipping container,...
They can also be attached below the wing of a large aircraft and flown with if there is no room in the cargo area.
(stolen from this question ) Notice the extra engine on the near wing.
aviation.stackexchange.com/users/609/ratchet freak
The Conroy CL-44 "Skymonster" was built for the purpose of transporting three Rolls-Royce RB-211 engines.
It was a derivative of the Canadair CL-44 and was meant to transport the engines for the Lockheed Tristar .
Jack Conroy had before modified old C-97s to Super Guppy transporters, and those initially transported Saturn rocket stages for NASA.
The picture below was shamelessly copied from the Wikipedia article.
Note the bulges near the tail: They cover the hinges for the sideways opening fuselage.
Today, Boeing 747 freighters can swallow most engines, so in the age of widebody transporters there is no more need for special aircraft for engine transport.
aviation.stackexchange.com/users/1961/Peter Kämpf
Having lived for nearly 15 years around the Boeing factories in Seattle, it was a common sight to see a flat-bed truck with a tarp-covered engine driving up and down the freeway.
Just like other big industrial machinery, they build a mounting for it, put it on a truck, and drive it down I-5.
aviation.stackexchange.com/users/43/abelenky
It's apparently pretty hard to get outer engine dimensions, but based on fan size and adding a bit, all but the largest engines will go on a standard truck.
Oversize permits are readily available.
Rolls-Royce makes engines in Derby (amongst other places) but not at the airport.
( East Midlands airport has one runway, 8200 feet, which is a bit tight for a 747.)
Therefore, engines must leave the factory by truck at least once.
I expect that the decision to send the dud engine for service by truck, boat, on the wing or in the hold will be purely economics.
aviation.stackexchange.com/users/1632/paul
Jet engine transportation is a highly specialized task, the primary method is ground transportation via truck and trailer.
It is important that the transport company uses fully air-ride trailers and advanced load securement techniques to ensure zero stress on sensitive engine components.
Peter Kämpf - While you are correct that some engines can fit inside of an aircraft for transport, the cost for this service is enormous when you compare it to a truck and trailer.
Also larger engines such as the Trent 1000
(Fits on a 787 Dreamliner) will not fit inside of an air cargo carrier.
aviation.stackexchange.com/users/3824/AircraftTransportSpecialists
One of the optional services in  Rolls-Royce TotalCare  is "Engine Transportation"   This service includes routine transportation of engines between the customer’s main base (or designated station) and the engine shop, and/or remote site transportation.   Jet engines can be very large heavy and expensive items. How are they transported? Are they flown or do they use road transport? Are there dedicated vehicles?
How are off-wing jet engines transported?
aviation.stackexchange.com
<jet-engine><aircraft-maintenance>
aviation.stackexchange.com/questions/8339
aviation.stackexchange.com/users/1289/RedGrittyBrick
Jet engines are usually transported by truck and trailer. Most will fit inside a wide-body plane or they can be shipped by container. In the past special planes were built to provide this service. Flat-bed trucks can be used to transport the vast majority of jet engines. However, engines can also be transported on aircraft - either in the cargo area or below the wing of a large aircraft. Specific examples of aircraft that can transport engines include the Conroy CL-44 "Skymonster" and Boeing 747 freighters.
Flat-bed trucks can be used to transport the vast majority of jet engines.   Jet engines can be transported on aircraft - in the cargo area or below the wing of a large aircraft. Specific examples of aircraft that can transport engines include the Conroy CL-44 "Skymonster" and Boeing 747 freighters.