Changing the frequency of your RC toy's radio signal becomes necessary when operating multiple vehicles in the same area, as some signals can interfere with one another. Most RC toys come equipped with two radio frequencies to choose from with only the flip of a switch, but there are times when the included frequencies aren't sufficient to avoid the interference problems. For those times, you'll have to do a bit more to change the frequency of your RC toy than flip a switch.
Purchase a crystal set from a hobby shop online or locally. Make sure that the crystal set is a matched pair with a crystal for both the transmitter and the receiver, and that it is usable by your particular transmitter and receiver system.
Open your RC vehicle to access the remote control receiver. You can open most vehicles by removing a set of clips that hold the vehicle body to the chassis. Some will require you to unscrew the body first before removing it. A Phillips head screwdriver is usually required.
Locate and remove the current frequency crystal from the receiver, slipping it out of the receiver housing. The crystal should have a tab attached to a small metal body which plugs into the receiver via two small prongs. Pull it gently from the housing so as not to break a prong.
Place the new crystal into the receiver, plugging it into the two small holes. The proper crystal in the pair should be labeled with an "Rx", to note that it is the receiver crystal. Replace the car body.
Remove the case from your RC radio transmitter, using the screwdriver.
Locate and remove the current frequency crystal from the transmitter.
Place the new crystal, labeled with a "Tx" for transmitter crystal, into the transmitter. Replace the transmitter case.