How do I remove Remote Managment from my iPad?

You cannot. Only the people or firm who installed it can remove it. And Apple cannot help with this if you are not the original purchaser.

If you bought the device used, you were scammed. Return it for a refund. Also see this excellent article about buying used Apple devices:

The All Too Common SAD Reality of Buying … - Apple Community

You can't, as it is managed by the company and you need to contact to their IT admin to remove the management.