A backed-up or slow-flushing toilet can happen for various reasons. Something might have been flushed and is blocking the pipe (see our FAQ on "What Not to Flush"). If the problem toilet is on the second floor of the house, this kind of internal blockage is the most likely cause. If your neighbors also have the same problem, the problem could lie in the city sewer main – call the local sanitary district or the city public works department to report the problem.
The first step is do-it-yourself – use a common plunger. If plunger pressure doesn’t get the water moving, the problem can usually be fixed by snaking the line. You can use a snake yourself, but basic snake tools at the hardware store might not be long enough, or powerful enough. Your slow toilet problem might need attention from a service professional who can use a power snake or hydro-jet tools to cut through the blockage in the sanitary line, and then use a video camera to diagnose the source of the problem.