There is indeed!
If you are simply replacing the graphics, you can double click the sprite and load the graphics in.
If you created a new sprite that has a different name and you want to replace the other sprite with the new one and the old one has events associated with it then do the following:
1. Back up your project.
2. Go to your event sheet(s) and search for events using the name of the sprite you want to replace.
3. Highlight all events that are returned and right click them
4. Select replace object. Choose the object you want to replace and then choose the object that is replacing it.
You need to make sure the new sprite is exactly the same as the old one. This means it has to have all of the same variable names, behaviors, applied effects, and so on. Construct will only allow you to replace objects if they are identical (besides graphics and collision polygon... but you would need the same number and names of image points too (I think)).
Anyway, best of luck! I hope that helps.