That's one way. The other way would be to EQ it.
Sorry, cruel joke of me for a simple typo. Couldn't resist though. Cheers!
But you were actually right. One could SQ the source or the amp. Another way would be to EQ the source. A third to mod the phones.
But I'd only mod phones I like though, IMO modding isn't gonna turn phones you don't like into ones you do.
Like Up Late said, with software.
Depends on what player you're using.
Are you on a Mac or Windows computer?
Do you use iTunes?
If iTunes: in the menu bar choose Window, Equalizer. There you have it. Switch it on and play with the sliders.