The Mac OS X v10.11 El Capitan currently being in the beta stage, it is recommended that a new partition is installed and the new OS X booted alongside the OS X Yosemite or Mavericks, rather than it being directly updated.
Doing this will ensure that the new OS X version remains separate from the previous stable build, while allowing you to boot between OS X versions.
Should you be interested in dual booting the OS X v10.11 known as El Capitan and OS X Yosemite or Mavericks, check out the following guide that details how to create a new partition to install El Capitan and dual boot your Mac.
Before you jump into the guide ensure that your device meets the following requirements.
IBTimes UK will not be held liable for any damage to the device which occurs during the process. Proceed with extreme caution.
Ensure that there is sufficient hard disk space to create a partition on the driver. Install OS X El Capitan to a new partition. You should have at least 40GB free space for this, and a minimum of 20GB for El Capitan. With less disk space running either of the OS X might affect the performance.
Do not forget to create a backup of your Mac with Time Machine. This process of partitioning a Mac and installing a new operating system could wipe out all data of your device.
OS X El Capitan installer. Click here to know how to create bootable OS X Capitan beta USB installer drive.
And of course a compatible Mac.
With the El Capitan running on an alternative partition of your Mac, you can always switch between the operating systems by rebooting and then hold the Option key. This will open the startup manager before OS X loads up and you can choose between either version of the Mac OS X you wish to go for.
This method is safe enough to test the OS X El Capitan on a Mac that is running a stable version of the OS X.
If you wish to delete the beta El Capitan and reclaim disk space go to Disk Utility and remove the partition. Do not forget to create a backup before you perform this.