I need OSX 10.9.3 for Beats !, I have 10.7.5 what do I do?

Open the Mac App Store and try downloading Yosemite. If you get told it's incompatible, you can't use that application.

Back up your data and check your applications for compatibility before upgrading.

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See if your Mac can upgrade to v10 Yosemite > How to install OS X Yosemite on your Mac - Apple Support

There's no point in installing v10.9.3 Mavericks if your Mac can run Yosemite.

Yosemite is free and available from the App Store.