If you do a search on here for coolant change you will find a pdf article from toyota describing all the steps.
Its pretty straight forward, ill have a go but read the article just in case i miss a step.
1 take the spare and the plastic surround off in the frunk.
2 find the 2 clear plastic tubes and attach one to the heater bleed valve, right under the windscreen with a white plastic screw thing on.
3 attach the other hose to the radiator bleed point on the top right hand corner of the radiator.
4 make sure they are vertical(ish) and attach them to the frunk holder upper
(no idea what its called haha)
5 undo the coolant cap
(make sure engine is stone cold)
6 loosen both the heater bleed point and the radiator bleed point, you should see coolant appearing in both the hoses
7 fill it with a non alcholol based coolant until the levels of coolant in the hoses are level with the coolant fill point.
Make sure the car is parked on an even surface.
This step could take a while and its a good idea to give the car a bit of a shake to make sure the coolant gets round.
Fill until the coolant is up to the filler neck ie full.
8 put the coolant cap back on to 1 click
(not fully tight) and tighten up the bleed points then take of the hoses.
9 run the car at a steady idle for a couple of mins
10 repeat the stages above to make sure its totally full.
Hope that helps, Ive had to do it a few times.
Sounds like you may have an airlock, the coolant you are seeing is being pi$$ed out the expansion tank.
If its still over heating after this change the thermostat.
