Hello,
This depends on your hosting environments, shared clients should be able to modify it via CPanel from the php zone editor feature if provided. Although are unlikely to have direct access, the same applies for shared resellers.
However, the ability to change the php.ini files is completely up to your hosting provider, especially on a shared hosting services.
Did I satisfactorily answer your question? Don't forgot to leave me a thumbs up or 'thanks'
If I didn't please send me a message, so we can discuss any issues with my answer. If there's any additional questions, feel free to ask them in the thread, quoting me if necessary.
Best Regards,
Kieran Cairns