A designer provided me with a finished design and provided the psd, eps and ai files. I'd like to make some minor changes in PS and would like to access individual layers - e.g. the text, background, etc. When I open the psd file, however, it only has one layer. how do I break out the original layers so that I can edit them?
once the layers have been merged, we cannot break them up
You can't. Once it's been flattened, you can't unflatten it. Talk to your designer: he/she will most likely have the unflattened version available.