I agree wit the coolant overhaul but that can get pretty expensive. Just wondering why you would refill the coolant??? But, I've learned thru out the years theres a few ways to do it right. Completely drain out your coolant, be sure to buy 50/50 and DONT use concentrated coolant or tap water. Take off your expansion tank cap, check it also to see if its damaged.
Loosen the bleeder screw and take off the hose on the TOP of the radiator.
Start adding coolant in the expansion tank, when you start to see the coolant come out the upper hose, reconnect it and continue to add coolant.
When the expansion tank is filled start the car, put your heat on high coming thru all vents.
after some time you should see the coolant rising in the expansion tank, when it starts to reach the top put the cap back on(leaving the bleeder screw open but not off/out) let all the air come out the bleeder screw til it starts to flow coolant this can take some time so have patients lots of it. I normally drive around the block a few times to get the car at normal running temp. If you do decide to run it around a bit make sure you CLOSE YOUR BLEEDER SCREW first. Make sure to bleed all the air out the system cause if not, it will make your car over heat no matter how much coolant you put in it. It you done everything and it still over heats, ill let you kno whats the next step ill take.