How to change service-account of reporting services at all levels

[amirameen]

We are running reporting service 2000 on server farm
my farm settings are as below

-reporting service run on SERVER1
-sqlserer 2000 database on SERVER2
-reporing service are running under application pool (configurable domain user account) for example:
DOMAIN1\sql.reporting
-company current domain name is [DOMAIN1]

NOW company has changed its domain name to [DOMAIN2].so my service account become DOMAIN2\sql.reporting

My real question is how can I change my reporting services to run under different domain account (without reinstalling reporting service)
can someone guid me step by steps from start to end

thanks in advance,
Amir