By default Photoshop allows you to switch between tools of a specific group by holding down the SHIFT key and pressing the letter that represents the tool. So for example, the Dodge, Burn and Sponge tools can be activated by pressing the letter ‘O’ on the keyboard, and then to move between the tools, use the SHIFT +O combination. So if the letter ‘O’ activates the Dodge Tool then pressing SHIFT + O will activate the Burn Tool, and pressing it again will activate the Sponge Tool, you get the idea.
Now that’s all very well but I’ve always found the SHIFT key a bit of an unnecessary step. To remove the need for holding down the SHIFT key when switching between the tools, open up the preferences dialogue box by going to Edit > Preferences > General (Photoshop > Preferences > General on the Mac).
As you can see in the illustration below, find the ‘Use Shift Key for Tool Switch’ option and turn it off! Click OK to exit preferences, now every time you press a letter to select a tool group, you can simply press it again to activate the next tool without requiring the SHIFT key at all.
Personally, I prefer to work this way. I find it quicker and easier to navigate to the exact tool I want simply by hitting a few keys on the keyboard!