Help - Garmin

[xtermin8or]

I have a Garmin streetpilot c510 - because of a lack of space I only loaded it with Gauteng and KZN maps - now I realised that there are maps of Europe and China on it as well - how do I delete these maps to free up space so I can load the rest of SA onto it

any help will be appreciated

P.S - the user manual is useless