When you first start playing Quadropus Rampage, your quadropus is quite frail. The upgrades page is where you (obviously) upgrade your Quadropus to become much stronger. There are 7 different types of upgrades, each affecting different stats of your quadropud, and each having 6 levels. The order in which you invest in upgrades is up to you and your playing style, but I would strongly suggest buying vitality and attack upgrades before any others.
The cost to upgrade per level is:
Upgrade to level 2: ????
Upgrade to level 3: 1,200 orbs
Upgrade to level 4: 2,400 orbs
Upgrade to level 5: 4,800 orbs
Upgrade to level 6: 9.600 orbs
Buying the rampage upgrade will boost the duration and damage of your quadropus's rampage, as well as lower the decay of the rampage meter. I would recommend investing in the other upgrades before this one, as you won't be killing enough enemies early game to rampage very often anyway. As you get deeper though, this is a very useful upgrade to have!
Investing in the bubble upgrade will allow your bubble ability to last longer, and give it a shorter cool down between uses. This should probably be one of the first upgrades you purchase after maxing out attack and vitality.
This is one of the best upgrades to get early on. Buying into the attack upgrade will increase your damage, critical hit damage, and chance to land a critical hit.
By getting the agility upgrade, you will increase the run speed and dodge cooldown of your quadropus. When to buy this ability depends on your play style. If you prefer to dodge and dance around enemies like a ninja, get this upgrade before bubble, but if you prefer to bubble and take hits like a tank, than get bubble before agility.
Bingo is your quadropus's beloved pet starfish. Upgrading bingo will improve his damage, knockback, and run speed. This upgrade is more of a luxury as your quadropus is the one doing the real damage, not bingo. Once bingo is fully upgraded however, you will notice that he is quite the formidable fighter himself.
When you get the vitality upgrade, your quadropus becomes much more resilient. By investing in vitality you improve your quadropus's max HP, toughness, and how much heart fish heal you. I strongly suggest getting this early.
The smash upgrade will improve your quadropod's smash ability by lowering the abilities cooldown, increasing it's damage, and increasing it's radius. It's a good ability and you should consider this upgrade once you have the more "urgent" upgrades maxed.
My suggested upgrade path:
If anyone has anything to add, please feel free to comment below.