usu one month notice in writing. I ususally call and email too, written is always better but phone call is faster. no need to go thro agent.
check for damages before giving back deposit. read your original contract when you have to pay the deposit , some wrote pay back one week or 10 days after keys are returned and some say immediately.
Also tax department may ask for proof of handover date for tax reporting, so ask the tenant to sign a confirmation letter for tax purpose.