Delete your account is at your picture (top right) > Account > Danger zone > Delete my account (or > Security & Legal > Delete My Account, which takes you to the same place). Type your email, ATOM sends a 6-digit code to it, and entering the code closes the account.
RIGHT AWAY: you are signed out on every device and nobody can sign in to the account again.
WITHIN 15 MINUTES, ERASED FOR GOOD: your account, and every tour you own, for everyone on those tours: schedule, day sheets, contacts and personnel cards (passports, medical notes), money (settlements, expenses, cash, per diem, pay), files you uploaded, guest lists and the rest. Also your community profile, friends list, usage record and recommend answers. Messages you sent in direct messages are blanked; the other person's side of the conversation stays. It cannot be undone, so download anything you want to keep first (your picture > Security & Legal > Download My Data).
WHAT STAYS: a tour someone else owns keeps its own card about you (its owner manages that); you are taken off its rosters. Records of the access you approved (for example letting ATOM support view your account) are closed and kept as proof of what you agreed to. ATOM keeps an anonymous count that an account closed, with no name or contact details. Backups roll off within 30 days.
ON A TOUR YOU DON'T OWN: deleting your login does not delete that tour. Ask its owner to remove your card if you want it gone.