Do nothing. Literally. Well, maybe click the upgrade buttons. If you're rich enough. Which can only happen by... Doing nothing.
Very pre-pre-pre alpha... Not developed that much, but expect a lot more. Also: Yes, upgrades work, it's just you have to buy a lot to see a significant difference. The bar speed upgrade after level 6 should naturally start giving less due to the lag, especially if you own the 2nd and 3rd progress bar. I planned this that way (not really, but it worked out.)