To do it correctly you will need a 44mm wrench/socket, a spring compressor, and a 10mm rod puller. The oil level needs to be measured with the spring and guide out. (148mm from tube top to oil level, with the fork compressed). I would not do a dump and replace, as you are guessing at the amount of oil you end up with. I remove the cap after removing the fork because that is the only way to fit a socket on squarely (easy to mess the hex). I used a wood clamp to grip the fork. You could also raise the fork in the triple tree and reclamp it to loosen the top cap.
The ES can be messy, as the left fork has compression damping and the right is rebound damping. When you pull the right rod out for reassembly oil will come up the rod puller. Pull too fast and oil goes every where. Note the small hole in my rod puller to let the oil drain. (again pull slow!) The rod puller is actually a lamp electrical conduit and connector. This 1-3/4" socket is a bit big but got the job done. Hard to find a 44mm socket or even a wrench that goes that big.
One more lesson learned, make sure the brakelines stay on the right side of the left fork during fork reassembly. If you have tied the left caliper back out of the way, you won't realize you messed up until way too late.
If you do not have any fork seal issues and are looking to do just change the oil a simple dump and run is perfectly acceptable.
Yes it is preferred to remove the spring and set the oil level rather than by volume. But if you take your time, drain completely and accurately add the correct amount of oil this Job can be done very quickly and easily without removing the cap.
Carefully measure what you remove from each leg and record it. Compare this to factory spec for oil volume.
I like to hang my forks for a few hours to make sure I get as much oil as possible out. I have done my forks several times and know exactly how much I need to add. Sometimes I set oil by level, other times I just do a dump and fill. The most important part is to get it done. A few mm/ml more or less in each fork will not make a noticeable difference. It will only change the air gap and therefore the air spring effect. This only becomes noticeable at the very bottom of the stroke. Not a place most reach that often.
Here is a link to a video of a simple dump and run on a set of cartridge forks. They are not the same as your es forks, but the procedure is exactly the same. It is a good idea to also check for rust or dings on the chrome before you loosen the cap. You would not want to slide the seal down and damage it during your maintenance. The lubing of the fork seal at the end of the video is a great idea as well.