Yes, you would use a bespoke tool designed for flashing, for example KESS or KTAG. For very old cars you can use a very cheap Galletto cable.
Reading the map is only the first stage, the second question is how to actually access and change the map - this is the incredibly difficult part
Maps are literally just hexadecimal - the numbers 0 to 9 and A to F. To be able to take nothing more than this and turn into something understandable you need software for remapping, I.e Winols. For the old diesels that had a EDC15 ECU, there was a free tuning program, that in combination with a free 1.9PD tuning guide online, would quite easily let you experiment with tuning at home. I had a Fabia vRS that I would constantly tune and then log and then tune. using a website like ecuconnections you can have other people review your map and give an opinion
pretty much all ECU programming software is expensive and even then you are not done, you need a DAMOS to be able to identify all of the maps on the ECU and adjust the values.
sure, you can purchase cheap maps online, but most of them are more of a decalibration rather than a performance remap. A lot of people think they are getting something decent when they go to a place with a dyno, but most of the time they take a generic map, make very minor changes and then call it a custom map, a proper custom map takes hours of work
if you are only interested in improving your car rather than getting into tuning, then the best option would be to go to someone like Celtic tuning that can come to a home address or work and flash a map. REVO are absolutely brilliant so if you have a local dealer, they are the best option.