Signers on a joint account are making an agreement with a bank that each participant is responsible for all fees, charges, costs and losses resulting from activity on the account. Banks protect their interests by not allowing a signer on an account agreement to have her name removed from the account without closing it, unless specific conditions exist.
Death of a Signer
Joint accounts usually have a "right of survivorship" clause. If a signer dies, then the remaining signer gains control of the account and all of its assets. The surviving signer can usually remove the name of the deceased party from an account by presenting a death certificate to the bank.
Written Agreement
Some banks allow a signer to be removed from a joint account by written agreement. For example, Santander Bank allows parents to remove themselves from the student accounts of their children, provided the parent makes the request, the account is in good standing and the student is over 18 years old.