My Volvo dealer only sells the concentrate. It should be mixed with distilled water. Never mix with tap water and never 'flush' the system with tap water (garden hose).
Not sure what the red one is, but it is advised not to mix coolants.
Therefore removing all old coolant would be advisable. The radiator has a plastic peacock that's rather fragile but may try undoing it first - I think it takes a torx T40.
Then at the rear of the block there is another 13mm deep socket (or wrench) peacock which will remove a little more coolant.
Then you have the heater core. Together with it's pipes/hoses, it keeps another almost 1L. Sounds excessive, but the best would be to remove the heater core, drain it and rinse it with some distilled water, then put it back in place. It is not that hard to remove,
https://www.youtube.com/watch?v=37u_oQ0Q0Gc with the mention that at 30:35 pull the coupler and upper shaft all the way down and remove it from the car completely - don't forget to mark the splines at the steering column so as to insert the coupler into the shaft at the exact same rotation/position