[H4R0015K]

What you will need:
1) Rooted Android Phone.
2) Busybox (Free - get it from market)
3) Terminal simulator (Free - get it from market)

Process :
1) Install both apps listed above.
2) open terminal.
3) type 'su' (without quotes) and press enter (it will give you root access)
4) now type 'cd system/app' (without quotes) and press enter (it will change your current location to location where system apps .apk's are stored)
5) now type 'rm <appname>' (without quotes) and press enter (this will remove the app)

Note:
1) make sure to make a copy of .apk before removing it.
2) if you don't know the app name then when you are in apps directory type 'ls' (without quotes) and press enter (this will list all the .apk's pressent in that directory.

[god20spy]

What you will need:
1) Rooted Android Phone.
2) Busybox (Free - get it from market)
3) Terminal simulator (Free - get it from market)

Process :
1) Install both apps listed above.
2) open terminal.
3) type 'su' (without quotes) and press enter (it will give you root access)
4) now type 'cd system/app' (without quotes) and press enter (it will change your current location to location where system apps .apk's are stored)
5) now type 'rm <appname>' (without quotes) and press enter (this will remove the app)

Note:
1) make sure to make a copy of .apk before removing it.
2) if you don't know the app name then when you are in apps directory type 'ls' (without quotes) and press enter (this will list all the .apk's pressent in that directory.

is more simply:
download this app from HERE
open the app,go on more->settings->check "root explorer" and "mount system folders"->push the "up" button until is grey->go on "system" folder->"app" folder,and then delete/move any aplication(is usefull if you want to make the reverse thing)
have fun