How Do I Reset My Ecu???

[TOMTOM]

HI all, how are you?


as some of you might of read my previous thred
about the engine check light and airbag light

the engine check light was on because i had a failed lambda o2 sensor,
i have just changed it but the engine light is still on...????

dose any1 know why this may be?

also how do i reset my ecu system?
can this be done by disconecting my battery terminals?
if so how long will i need to disconnect?

and by disconecting battery it wont do any damage to standard fiat punto alarm system or not let the car start after reconecting?

sorry for all the questions just wana make sure.

thank you in advance.