Replace work item 
Using this button, the current work item, can be replaced with another. Choose the work item you wish, and close the window by clicking «Select»
Replacing the
work item does not affect the «Formula» field, which remains the same. This
command is really useful if you have chosen by mistake, one work item instead of
another, or if you want to replace a work item without necessarily delete the
link and then add a new one, filling again the formula field.