Can I change the articles of association of my UK company?

In short, yes you can.

But once a UK company is formed then it needs to change its articles of association by a special resolution which requires the consent of 75% or more of the shareholders or the company's officers.

If the articles are changed then there is a legal requirement to notify Companies House within 15 days of the resolution being passed.  You need to send the special resolution along with the amended articles of association (showing where they have been amended) to Companies House in order to comply.