From any tab on the MetaTrader application, tap on the menu expander icon to view more options. 

Under your Live MetaTrader account information, tap on Manage Accounts.

Tap on the icon next to the plus symbol. 

Tap on Change Password.

Select Change master password in the first selection box.

Type your Current password (Master password).

Type your desired new password and type it again to Confirm. 

Tap on Next.

A text box confirming your change will appear.

Tap OK.