Portal Migration

Hi all,
I’ve transferred the content of a WordPress based website from Altervista to a new domain.
I’m encountering the following trouble: when I try to login and when I click on other links I become redirected to the old domain and I don’t succeed in going on with the activity.
Could you please explain me what should I change ?
Probably the reference to the old site are still present in local variables such as site_url.
Where should I search the string to edit ?
Thank you,
Camillo Bosco