deere x739; exmark quest 42" zt

Hi all. We have had our eXmark 42" ZT, model QTS691KA422 (ser no 314631306), for about 8 years, and the tires have since lost some significant traction. We were thinking it is time to replace them. Also, one of the old tires has a slow leak, another reason to replace. Tire treads are...