How can you remove demo games Sony Ericsson?

Built into the base load by either the carrier or sony ericsson.
Only way is to root kit the phone - try XDA or Android Dev forums.
Word of warning to the unwise you void your warranty and can brick the phone.

That said despite trying haven't managed to brick mine yet - just make sure you maintain connection and power through any flashing. (And yes the built in bloatware is incredibly annoying till you get rid of it)