Within certain narrow parameters, the touch can be adjusted by regulating the action. Regulating is the process of restoring the dimensional relationships (positions, angles, distances, etc.) of the action parts to their factory-specified defaults. Over time and with playing, these dimensions gradually change and must periodically be restored in order for the piano to function properly. Each dimension also has a certain narrow window of permissible variation, so by cleverly manipulating these variations, it may be possible to make the touch slightly lighter or heavier, or the repetition faster, than the factory default specifications. Lubricating the many friction points in an action can also work wonders in lightening a heavy-feeling touch.
If changes are desired that fall beyond what is possible through normal regulating and lubrication, then the technician must carefully analyze the source of the problem and make more drastic changes to the action, which may involve modifying or rebuilding it to some extent. This was once solely the province of trial and error, but scientific principles can now be brought to bear on these problems, with consistent and happy outcomes. More advanced and technologically-savvy technicians can advise you about your options.
Note: There is a psychological connection between tone and touch. Sometimes adjusting the tone of the piano, or just tuning it, can make the piano’s touch feel better, even though there is no mechanical connection between tone (or tuning) and touch.