First, with the Premiere project closed, move the original files that you're editing with to a new folder or other location. Open your project and it will warn you of missing files. Click the Relink others automatically checkbox and then hit Locate.
Navigate to the folder with the new graded footage, find the first clip and press Ok. It will then re-link all the other files to the matching files in new folder.
Note that this will only work if the files have the same name. Different extensions are ok, from my experience it's smart enough to deal with it if your original footage was an MXF and you're replacing it with an AVI for example.
In your project window, or in your timeline, select all the files you want to replace, right-click and choose Make Offline. Generally you want to choose "leave the media files on disk" in the dialogue that opens, because it permanently deletes the file if you don't.
Once your clips are offline then you can re-link. With all the files still selected, right-click and choose "Link Media". This will open up the same dialogue as method 1, so as before you choose Relink others automatically and navigate to your graded footage.
Again, this only works if the graded clips are named the same as the originals.
With the project closed, move the original clips from where they are on your hard drive, and replace them with the graded clips. When you open the project it will link to the new clips, again, provided that they are named the same. You will need to re-render any rendered clips in your timeline.
Another note is that if your footage contained audio you need the graded footage to contain audio, even if you're not using it. Premiere won't accept them otherwise. So in Resolve, make sure you check the "Render Audio" box.
I use this workflow when I'm working with BlackMagic Cinema Camera footage. DaVinci Resolve gives me much better results than the Adobe grading tools, either in Premiere or Speedgrade. The only thing that does nearly as good a job is using Adobe Camera Raw by opening the footage in After Effects and rendering out intermediates, but that is extremely tedious and dog-slow.