I am in taqleed of Ayatollah Sistani, however, I find Ayatollah Khameenai’s rulings on matter more credible so I want to change my taqleed to him moving forward. Also, here I would like to mention that I never truly made the decision of Taqleed and just followed what my parents did. Now that I am older and more mature, I want to make my decision for taqleed and follow Ayatollah Khamenai’s rulings.

You cannot change taqleed except if you come to know that the another mujtahid is more knowledgeable and pious than the present one. If you confirm and certain, yes you can