I am very new to salesforce, and even newer to Apex.  I'm trying to update a field on my account object, after an opportunity has been closed - won. Here is my first attempt;

trigger AccountTypeUpdate on Opportunity (after update) {
   
    Account myAccount=trigger.update[0];
    if (opportunity.StageName = 'A - Closed Won') {
     myAccount.type = 'Customer';
     update myAccount;
    }    //else nothing
}

Evidently it doesn't work, and I realize I would have to select the account associated with that opportunity, I'm just not sure how to go about doing that.  Any help would be greatly appreciated.