Three days short of a full month ago, Apple released its first-ever public OS X beta for its upcoming Yosemite (10.10) release. Today, the company has followed-up with a new build, which closely matches the Developer Beta 6 release that came out earlier this week. While Apple highly recommends that everyone using Beta 1 update, it hasn't provided us a changelog; it'll be up to you to find out what's new, although you can expect that much of what changed will boil down to bug fixes.
Ars Technica wasted no time in giving Beta 2 a test, and noted that aesthetically, some noticeable things have changed. The volume slider, for example, now matches the frosted translucent look of the rest of the OS, and if you open up System Preferences, you'll notice that more updated icons have been rolled-out.
If you already have Beta 1 installed, you won't have to completely reinstall the OS to update. Instead, you can simply use the built-in OS updater. If you haven't touched Beta 1, but instead wanted to wait for a bit of refinement, you can still sign up to become a tester at the URL below.
Apple hasn't said how many individual betas of Yosemite it will be releasing, but as the OS isn't expected to launch until later in the year, I think it's safe to say that we'll see a Beta 3 next month.