you don't have to have the head checked but its recommended. the head bolts are supposed to be torqued in counterclockwise order from the inside bolts to the outside bolts. torque them in order in three stages to 18 ft/lbs then to 27 ft/lbs then an additional 120 degrees except the front right stud which you torque to 90 degrees
Changing a head gasket (or in your case, gaskets) is a long process. If you have to ask this question, then you probably do not have the tools and knowledge to complete the task. A service manual would be necessary for you to have the correct procedure and torque specifications.
I assume you mean the valve cover gasket. You replace it by removing the valve cover and cleaning off the oil gasket and the mounting surface. The install the new gasket and reinstall the valve cover. Tighten it to the specifications the manufacture of your engine recommends.
If the light is on, it will need checked and diagnosed.
Have the heads and head gasket checked possible thermostat in backwards
Replace gasket why does gasket keep sliding
replace head gasket
take off the head, replace gasket. reinstall head
What is the cost to replace the head gasket on a Mazda MPV?
cost to replace a head gasket
To make sure it is a match and therefore the correct gasket for the engine.
I would recommend getting a chilton's manual. not to tough of a job, just make sure you have you heads checked.
The Intake gasket is leaking, NOT THE HEAD GASKET. Replace the intake gasket