I have replaced many of those, and as was said, most POCO's will require the whole meter base changed, at least here they do if any upgrade has been done, those old meters are only 15 amp 240 volt, some are 15 amp 120 volt, I have seen these in a 30 amp 240 volt flavor also but the way they mount is all the same, most have slide bars right above where the line and load connections are, this was how the utility would disconnect them when non-payment happened, but please beware, all insulated tools are required with them, also the 4 setscrews just below the meter is what disconnects the meter base conductors but they will be hot if the slide bars are still down, after power is removed loosing these will allow the meter to slide up if it is the type on a hanger and come right out, some of these did have a meter socket behind it that accepted a regular meter, when we did a service upgrade we would turn off the power at the weather head, and pull the meter out, and re-install it in the new can.
The ones that just had wires coming out of them we would tie them back in at the weather head and use meter jumpers and a meter blank in the new meter and the POCO would reconnect the drop and install the new meter and put our jumpers and meter blank on top of the meter for us to pick up.
Just remember a meter is the POCO's cash register and some do not like them to be messed with or seals cut or taken apart.
I think they call them A-Base meters around here