/remote [on|off]] This switches processing of all scripts on/off.
Scripts are addons for mIRC to make look it better and/or add some (not always useful) features.
Click
here for more info's.
You can find a lot good scripts at
mIRCScripts.org.
Replacing is quite easy .. just uninstall your old mirc, and install a new one.
If you want a plain mIRC without any scripts look
here.
And DCC is as you said built in, so its not a script.