Is it the 'change oil' light, or is it the oil light?
If it's the change oil light, they may have failed to reset it properly. You may be able to reset it yourself by looking up the process on youtube - however if its the oil light, that usually only comes on when the oil is low enough that it may already doing damage to the engine.
Check the oil level by pulling the dipstick out, wiping it off, putting it back in then pulling it out again. If it is below the low level, then either they didn't put enough oil back in when they changed it, or the vehicle is using oil.
If it is low, either they didn't put enough in it, or the vehicle is using oil.