The Branch Manager,
Most respectfully, I am __________(Your Name) and I am holding account number __________(Mention your account number) in your bank __________(Name of the Bank) and my branch is __________(Bank Branch).
I am writing this email in order to request you for upgrading my bank account. Currently, I am holding a bank account with ________ (mention bank account type) and I am looking to change it to __________ (mention).
Therefore, it is to request you kindly guide me through the procedure. I shall be highly obliged.
Thankful as always,
____________ (Contact details)