i've purchased jcw grille on Amazon and I actually replaced lower grille pretty easily but the upper grille. I used 10mm socket to remove washer nuts and it spins but won't come off. how do i have to remove the washer nuts?

 

The nuts create a thread on the plastic posts. If over tightened (more often than not) they spin and strip the threads they've created in the plastic. If you wedge something (screw driver) between the back of the nut and the metal of the hood the nuts should grab and start coming off when turned with a wrench. It's hassle for sure.

 

Na, not so much.
I removed the "bar" grill (correct name ?), from my 05, R53. I tried something different on most every nut on my grill...nothing. I used an Exacto knife blade, a small screw driver blade to "help" the nut find or make new threads, a "very" thin wire cutter to "wedge" the nuts off as the nut was rotated... Nothing worked. I finally just used the thin wire cutters and cut the posts. And yes, unfortunately, that rendered the old grill useless.

Use care in what-ever method you use, it's easy to drop the nuts into un-findable locations. A large towel or something over the engine to catch the nuts and plastic washers. Though both are purchasable IF required..!

I also installed the JSW grill. I kinda like the grill with the smaller holes...may swap it down the road a little.

Mike