I want to modify a few icons in the theme.
How would I go about modifying them, and moreover where are they located?
Systemwide themes are placed in
/usr/share/kde4/apps/desktoptheme/ but you can copy to
~/.kde/share/apps/desktoptheme/ if you want to customize for a user.
KDE Icons are place in
/usr/share/icons or in
/usr/share/icons or ~/.local/share/icons`)
On the following link there's an nice example on how to customize a theme: https://www.kubuntuforums.net/showthread.php?56120-Customize-plasma-desktop-theme .