Reddit reviews Emerson Swan 1 8"Angle Steam Vent, Adjustable

The radiators in the hot rooms need smaller vents so they take longer to heat up, and/or the radiators in the cooler rooms need larger vents so they heat up more quickly. Some steam vents have a dial you can adjust like this, others have a replaceable orifice like this one - I got two of them last year and in spite of their low price they work perfectly. If a vent is not adjustable you can replace it with another vent.

Also, the headers in the upper floors may have undersized vents. My house has two headers. One is a short headers supplying 5 rooms, the other is a long header supplying 2 rooms. The rooms supplied by the long header took a long time to heat up, so I replaced the slower header's vent with one of these and it heats up much faster now. It cost me $75 if I remember correctly, but it was well worth it. It has much more venting capacity than anything with a similar price.

One last thing: see the diagram here: https://www.gorton-valves.com/products In general you want small capacity vents for radiators near the boiler/with short pipe runs and large capacity vents further away/with longer pipe runs so the system vents all the radiators at about the same time. It's part experience and part trial and error.