schengen visa single entry ,how to change to multiple entry

hi just want to one of my friend has been issued a single entry schengen visa for 90 days no of entries 1.
how they can get the multiple entries visa instead of single entry when the speak to embasssy which issued the visa they said visa cant be ammended they have to reapply again with all the requirements.and they did not visit it yet .
so my question is if they reapply will the embassy cancel old visa .
and grant a new visa with multiple entries .
or what happens thanks in advance for replying

and what if they travel on that visa can they get it done to multiple entries while they are in schengen or its not possible.