I want to change the brokerage account associated to an investment account. How do I do it?

Thanks!

What do you want to change? You can edit the account attributes by right-clicking the brokerage account in the Accounts tab. If you want to replace the brokerage account by another one, I believe you can do this simply by renaming them. I am not 100% sure, but I think an account is recognized as the brokerage account of an investment account if it has the exact same name, followed by " (Brokerage)".