Thread Subject: updating variable value from gui

Hello everyone;
i have created a gui that loads a .mat file and thus save all the variables in the matlab workspace. My second task now is i have 2 edit text boxes and a push button
--->what i want to happen is the user of the gui can enter the name of a variable already existing in the workspace in the first text box and then enter the new value of the variable in the second text box and click the push button (update) to update the value of the variable from the old value to the new input value
for example lets say the workplace has x=1, from the gui the user should be able to put x in the first box and then 3 in the second box and click update ...and the value of x=3
Thank you