RH Side

Remove the collector cover.
Disconnect the ground cable from battery.

Fig 1: Disconnecting Ground Cable From Battery
Courtesy of SUBARU OF AMERICA, INC.
Remove the air cleaner case. < Ref. to REMOVAL , Air Cleaner Case. >
Disconnect the connector from ignition coil.
Remove the ignition coil.
NOTE: Turn #3 ignition coil by 180° to remove it.

Fig 2: Locating Ignition Coil Connector Terminals
Courtesy of SUBARU OF AMERICA, INC.
Remove the spark plug with a spark plug socket.
Install in the reverse order of removal.
Tightening torque (Spark plug):

21 N.m (2.1 kgf-m, 15.5 ft-lb)

Tightening torque (Ignition coil):

16 N.m (1.6 kgf-m, 11.8 ft-lb)