Dethatching is done only occasionally, perhaps because the equipment is expensive. Rent a power rake at an equipment rental or hardware store for dethatching. A power rake weighs a substantial amount, so help with loading may be necessary.
Power rakes have steel blades or wire prongs with adjustable spacing and depth. The settings vary depending on grass type. Usually blades should be 1 or 2 inches apart for sturdy grass and 3 inches apart for more fragile grass. A height of about 1/4 inch is common, since the goal is to remove the thatch without destroying the living grass underneath. Ask for information about setting the blades from the rental store. Place the machine on a level surface when setting the blades.
Mow the lawn slightly shorter than usual. Water if necessary; the best results are accomplished when the ground is slightly damp.
Go over the lawn several times with the power rake. Change direction each time so that you cross previous paths.
Remove the loosened thatch by raking. The thatch can be recycled as compost or mulch if it has not been treated with herbicides or pesticides within the past month.