The steps to change the master password and investor password on MT4/MT5 on the computer are the same.
Steps: After successfully logging into the MT4/MT5 software, click on "Tools → Options → Server → Change → OK"
After clicking "OK" the change password page will pop up, if you wish to change the master password, you will need to enter the current master password, select "Change Master Password" and then input the new password, confirm the new password again and click "OK" to complete the changes.
If you wish to set up/change an investor (read-only) password, you will need to enter the current master password, select "Change investor (read-only) password", then input the new password, confirm the new password again, and click "OK" to complete the changes.