Grohe 28535 Unusual looking shower arm

[BJL]

Hi, I am a newbie, and have a questions about unusual looking shower arm.
I have recently moved to a new place, and found the shower arm/head like this. I think this is Grohe shower arm/head. I want to replace this with hand-held head and/or shower arm. I found out that angle from the shower arm is too steep to install regular hand-held shower head, so I may need to replace shower arm too. My question is how to remove and replace it with regular/standard shower arm, then, I want to attach hand-held shower head to it. I have dome shower arm replacement by myself, but this one looks very different. Do I need professional plumber to do the job? Any advice/help would be greatly appreciated. Thanks.

 

[Terry]

Inside the wall it's 1/2" thread to the adapter for the arm.
Once you loosen the allen screw, remove the arm, you will be able to spin off the adapter. You might need and easyout for the remaining nipple in the wall.