Step 1: When you create a new connection, for example as shown here Connect To hadoop , you will get to Preview Screen.
Step 2: On preview screen,on top right corner you will see a button of "History".
Step 3: When you click on History, a popup opens which gives you all the details of the transformations that took place recently.
Step 4: You have a cross button corresponding to each transformation performed. Selecting the cross, basically undone that particular transformation.