Tax Classification Change in MM17

Hi,

we want to change tax classification that defined in Material Master/Sales Org. 1 view from %18 to %8 for all FERT products.

I execute MM17 tcode and choose MLAN table from list and when i select a material and get into "Data Records to Be changed" i can not get old old values and enter new values.

how can i make this process ?

Thanks