Well, yeah but... the volume may still need to be changed due to it's 'apparent loudness' level. Other parameters may need to changed as well... after all, they're two different files with probably different start times, length and such.
That said, "View> Project Media" Right-click the exiting file you wish to change and select "Replace" from the drop down list.
There is a lot of different ways to accomplish the same end result though.