I googled remove+google+toolbar+mac and found people asking the same question, and getting blown-off. I'm not familiar with Apple enough to know a reputable website, and I'm not going to pick one at random where people suggest, "here's how--download this simple tool."
Didn't check that Apple website because I don't want to spend the morning there trying to find out the answer to a simple question.
What application is showing you the Google toolbar? Is it Internet Explorer Mac?
Apple's web browser Safari has an integrated Google search function. I'm very familiar with the MSIE Google toolbar problem in the Windows world, it's one of the limitations of MSIE that its default settings will accept executables without asking.
If the toolbar is only present in MSIE, I's switch browsers.
Are you talking about the Google search bar in Safari? If so, go to View, Customize Toolbar, and add or remove whatever you wish. I do not know how to put a different search engine in the toolbar. However, if having a different search engine in the toolbar is a big deal to you, download Firefox, which does allow you to pick from any search engine.