I am tryng to remove the existing carthridge on the front strut to replace it with a new one. is there a special key to unscrew it or can I just use a chisel and hammer?

Without the actual tool, use a pipe wrench or very large pair of Channel Locks.

I prefer the pipe wrench.

+1 on the VERY LARGE pipe wrench.

Some come easy and some come VERY hard. I'd avoid a chisel, unless you are going with the monotube bilsteins and have to replace the cap anyway.

Good luck.

Thank you guys