itch.io

Unfortunately, the only way to do that right now is by refunding the old 29.99 one and repurchasing, but I'm not sure the what's the time limit for refunding (I think too old of purchases can't be refunded anymore)

I am a customer that bought the game a few months ago. There is a link where they said that they are offering a refund [in case you were not part of the people who bought the other versions to get the beta access, too]. 

You just need to show your bill info you get after you buy the game to the email they provided in that page [You know the info you get your email, date, hours, and the amount it charged your CC], and you can then buy the $45 or $60 version. 

I bought the $60 version [the one that have the fanbook + the beta access]. Just go to the main homepage of this game and when you click the buy $29.99 or more, type $45 or $60 [the fanbook will be released in the release date] and you will have access to both beta access version [mac and win]