Hello Yasir,
it is easier to remove the buttons using ribbon work bench and not using unsupported JavaScript way. ribbon workbench helps you to modify The actual XML that controls the button. You can hide the button.
if you want to use JavaScript, use F12 - debugger that comes with ie to get the id of the button, then
document.getElementById("idofcontrol").style.display = 'none';
or use readonly to make the control readonl or use disabled property.
regards
Jithesh
j