I'm not understanding the underlying question here, please explain exactly what you hope to achieve and why.

My purpose is to cancel totally my current Hobby plan and start a new one so I can start a new Hobby plan

yes it's possible, from the billing account page, click manage subscription.

but may I ask what is wrong with your current hobby plan?

there's no problem but I use railway for an exam and my current usage is nearly expired so I want to renew it before his shutdown (until my professor correct it), thank you very much