With your ROM loaded, head to Tools ⇒ Hex Editor. A new window should pop up. Next, go to Options ⇒ Memory Domains and select System Bus. Also go to Options ⇒ Data Size and select 1 Byte. Navigate to the relevant address (e.g.
8011A644) by hitting CTRL + G or going to Options ⇒ Go to Address.... To make changes to the RAM, right-click the relevant byte and select Poke Address. In the new window enter the value you want to change the byte to and hit Poke to confirm. Your changes should be reflected in the game immediately.