Access - Get subForm datasheet value of row

I have a subform which is created with textbox and some command button in the top of the window, so this will simulate like a Datagrid.



http: // imgur.com/MpIpksT



This is how it looks my datagrid when it fills from a Query.



http: // imgur.com/kxAS8Ff



What I want is when I select a row from my subform, I want to Click the button "Cambiar", and get the value of the machine selected.



http: // imgur.com/LCEQlSI

Access - Get subForm datasheet value of row