Press the arrow on the right side to open the shop. click on a tower icon in the shop, and then click where you want it. DO NOT DRAG SHOP TURRETS. To upgrade, click on a desired turret and the upgrades will appear. Click on a trashcan while a turret is selected will delete the turret with 50% back. Click on a trashcan before placing a turret or while placing a turret will give you all the money back and stop placing it. You can increase the money a farm makes by upgrading its damage.
Thanks to my testers! @Accidental_Octopus The guy who made round 21 in easy mode --update logs-- update 1.0 added delta time added update logs