HELP NEEDED FOR GLK 350 MODEL 2010 TIRES UPGRADE SIZE
 

https://cimg3.ibsrv.net/gimg/www.mbw...0be35e94e2.jpg
I HAVE 20'' RIMS WITH TIRES SIZE :
245 / 45 R20 100H XL

WHAT IS THE MAXIMUM HIGHER TIRES I CAN GO FOR ?

I just upgraded by 19 in stock oem 235/50/19 rims and wheels to the 20x9.5 MERCEDES GLK350 OEM rims and wheel. Boy! What a difference. I love the stock 20 rims they are really nice I've got the Michelin Premier LTX 235 45 R20 with the rims and they are very nice with the rims. Hope that helps

my problem is not with rims size. it is with wheels size. my rims are 20'' already but the tires of 235/45 are thin and i already had 2 defects tires before due to off road drive.

What do you mean they are thin? Bald? Go to Discount Tire Direct and put in your model and it will show you what is available

sorry my fault with describing it thin. my tires are with width 255, ratio 45 and rim 20. so my issue is with the aspect ratio of it (45). i asked a dealer about putting 50 or 55 but he advised not to do it because the size i have is what fits my car for better performance...

Get some 17" rims for going off road. They look sexier with B.F. Goodrich Rugged Terrain or for more grip Mud Terrain.
You will never get enough tire in the wheel well for good grip with 20" rims. Your current tire height is 29.23 " with 694.51 revs per mile. A 255/60 R17 is the same height 91.23 and the same revs per mile so you won't need to change anything but will probably never have a problem with traction or faults, plus the ride may be softer. Of course on road extreme handling might suffer a little, but the car will look meaner!