There are basically two ways to fix a blown head gasket.
One way is to use a product like BlueDevil Blown Head Gasket Sealer. These are products that are mixed with water and added in solution to radiator coolant to heal the breaches within the gasket and to find out more about these head gasket sealers go to My Lab Guide.
The alternative is to remove the cylinder head and get it reconditioned in a machine shop then replace the gaskets and reinstall. This type of job is best done by a professional but can be done by an amateur who knows their way around a car.
If a professional mechanic is doing the job he will remove the head and send it away to be reconditioned and surface ground. He should check all ancillary equipment like radiator, water pump, belts, hoses, thermostats. While the head is off he can check the pistons for slap and make sure that the deck of the block is straight. It is also probably a good time when the engine is so stripped down to check timing belts or chains.
If an amateur does the job they can also send the head to a machine shop or they may be tempted to do more by hand. This will involve dismantling the head, buying lapping paste and using a lapping tool which is basically a round piece of wood with a suction cup and rubbing the valve seat to the valve seat insert to mate the two surfaces so no “blow by” occurs. The head still will need grinding (shaving, milling) to ensure it is straight and true so it can mate with the head of the block. Remember when re-installing, head bolts will need to be tensioned down to a particular “torque” and be done in a set sequence.