Generally you take the model number to the manufacturer's site and look up its specifications.
Now depending on what connection you are planning to use, a 4K monitor might only run at 30hz with this card, via display port. If your particular card doesn't have Display Port, but HDMI, then the same might be true, as it certainly comes before HDMI 2.0 was a standard.
Now if you plan on all four monitors, that might be beyond the cards capabilities.
GTX 550Ti is getting fairly old. GT1030 are about $90 and would make a reasonable replacement(s)