There are several questions about livery changes and livery in general on this website. Yet, I fail to find information about paint removal.
As a routine maintenance for an airframe that can live for up to 30 years, livery is redone several time as explained here. When changing painting, it should be preferable to remove the old one (I'm mostly thinking about weight as a big airliners has a lot a surface to paint). Moreover, I imagine that for military aircraft changing their operation theater, paint must be redone to adapt camouflage, and thus accumulating many layers of paint may have consequences.
Given material and other aviation-specific constraints, I also imagine there are special techniques to handle any intervention on the airframe.
Is this paint removal done and if so, how?