Much office equipment is still built for a standard-sized man, and is not downwardly adjustable for women or smaller people, or upwardly adjustable for tall people.
Foot rests can help some smaller people. Taller people can sometimes have their desks fitted with leg extensions to raise the work surface further off the floor, but some will need special desks or chairs.
If you find that your office furniture does not fit you, you should raise it with your line manager. If this proves unsuccessful and you work in a unionised workplace, raise it with your safety rep. Employers have a legal duty to provide furniture that does not injure you.