When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
There are lots of other posts on changing coolant.
If you do not want to flush the system, just open the drain **** on the lower right side of the radiator. You will get about 2 gallons out. Refill with a 50/50 mixture of dex-cool and distilled water.
The system holds about 12 quarts, so there is a gallon left in the block.
If you want to flush the system I would add distilled water, circulate, drain, and repeat until the water comes out clear. (meaning you have 4 quarts in the block of pure water)
To get the system back to a 50/50 mixture, add 6 quarts of pure dex-cool, then top off with water.