Based on ChatGPT docs, currently there is no way I can do so. But I am still interested in if it is possible to cancel my plan through customer service first then do upgrade. The current limit is too low for me.
Based on this Can I migrate my ChatGPT Free or Plus account over to ChatGPT Team?
If I were in your situation I would wait until they offer the option to migrate. If you cancel before having a second account you will lose all the information if it is of value to you.