I usually do it in this order
-Open Object Browser
-Highlight the object you want to replace
-Open the Replace Objects Screen
-click the 'from object browser' button for the top box.
-It should appear in the top white box.
-Go back to the object browser window, pick the object you want to replace the old ones with.
-click the 'from object browser' button for the bottom box.
Hit enter
That should have done it.
You probably already knew how to do that, if so i'm sorry I've wasted your time.
Bearing in mind, I dont think you can replace more than one type at once.