I have an old CTC and found removing the old filament less than perfect. I always snip the filament off and just keep extruding it and then feed the next
filament in as it runs out. Wait for the colour change and then its ready to go.

Saves having to pre-heat also if your ready to print. Less hassles with small stringy bits getting left behind or clogging the feed.

Does not waste much filament.