How to disable changing username and email by users?

Hello.
Please help me and say me:
How to disable changing username and email by users?
I see users in their control panel have abilities to change email and username.
I want to disable these abilities.

Does anyone want to guide?

1) remove links to these pages in theme
2) remove forms in theme files
3) it's good to go into core (controllers), search these controllers for changing user name & email and at start just add
return false;

It is no good and very bad that we can not disable changing email and user name in (user setting) section.

If designer of core of Osclass decided they only use several line code with a few if and condition and check box for insert this ability in core in user setting section.

Please report this important suggestion to programmers and designers of core of osclass.

Thanks

Fact that this question may be asked once a several years means it's not important feature.