Match an upgrade to your current obstacle
Check what each available upgrade says it changes. Choose an option that helps with the next rock or progression step shown in your session, then test the result.
Recheck rocks after improving
After an upgrade, revisit the rock choices currently available. The official description confirms bigger rocks as an upgrade goal but does not state an unlock order.
Balance progress with pet earnings
Pets earn money according to the game description. If that money is available for upgrades, compare the options shown in-game and choose based on your current objective.
No published upgrade prices
Exact costs, upgrade caps, multipliers, and best purchase order are not listed on the public game page. Treat community numbers as version-specific until verified in-game.