For passenger side - you will need to remove the air intake to gain access behind the head light. It is still a tight squeeze to reach the turn signal bulb even after removing the air intake piece. For driver side - you will need to remove the battery. After removing the battery you will find more room to work than the passenger side. Not a easy job for something as simple as changing the light bulb.
With a hammer
The 2006 Subaru Impreza has 39.7 in. of front head room.
The 2009 Subaru Impreza has 54.8 in. of front shoulder room.
The 2007 Subaru Impreza has 38.6 in. of front head room.
The 2012 Subaru Impreza has 52.2 in. of front hip room.
The 2001 Subaru Impreza has 51.8 in. of front hip room.
The 2014 Subaru Impreza has 52.2 in. of front hip room.
The 2002 Subaru Impreza has 53.3 in. of front hip room.
The 2003 Subaru Impreza has 53.3 in. of front hip room.
The 2001 Subaru Impreza has 52.6 in. of front shoulder room.
The 2006 Subaru Impreza has 53.3 in. of front hip room.
The 2007 Subaru Impreza has 53.3 in. of front hip room.