did it go smoothly? Will I still have to login to dsense using the old details or the new? I don't use the email account I signed up with and don't want to miss any emails from adsense if I were to get any
Once the email is changed you will login with the new email address. You will receive any emails from Adsense to the new email.
Awesome. I'm wondering now if I should wait until my first check arroives. I've been with adsense since 2005 but didn't use it for a couple years. Jan of this year I hit $100. Would I be alright to change it now or wait until my check comes so I don't risk delaying it's arrival?
Just log into your account and change your email now, it has nothing to do with delaying your payment's arrival. You don't want to miss any important email sent by Google.
Log onto Adsense Account. Go to 'My Account'->'Account Settings'. Click 'edit in Google Accounts' besides 'Login Information'. There you can change your login information.