How to change from Mavericks to Ubuntu?

So you want to go from OSX Mavericks to Ubuntu?
And you don't want to use a CD drive or a VM.....

The only solution I can think of is to try putting the .iso for the Ubuntu liveCD installer onto a USB thumb drive.

NOTE:
I'm not a Mac user and haven't been for a long time, so apologies if any of this is incorrect.

To get Ubuntu onto a USB drive, do the following:
- Download the .iso for Ubuntu.
- Insert the USB drive you want to copy the iso onto.
- If the USB drive gets auto-mounted by the OS, open a terminal and unmount it - if memory serves I think you need to use diskutil:
diskutil unmount /dev/yourusbdevice

NOTE: /dev/yourusbdevice is the device identifier for your usb drive. e.g. /dev/sdb1 << Important: Make sure the device identifier is the correct one for the drive! If you are unsure of the device identifier, you can use the following command:
diskutil list
Which should list the disks currently inserted.
- To copy the iso to the thumb-drive, use the dd command in a terminal:
dd if=path_to_ubuntu.iso of=/dev/yourusbdevice bs=1m
Where path_to_ubuntu.iso is the path and filename of the iso you downloaded and /dev/yourusbdevice is the device identifier for your thumb-drive e.g. /dev/sdb1.

Now you should have a bootable Ubuntu LiveCD on a USB drive.

At this point, I should point out that I've never installed Linux on a Mac before, so I don't know how well Ubuntu will work on your machine. But if it is an intel based model, it should work OK....I think! But before installing, you might want to test Ubuntu to see if it works well enough with your hardware.

If you reboot to the Ubuntu live CD on the USB drive, you will be presented with a menu and the option to install Ubuntu or to try Ubuntu without installing.

If you select the 'try Ubuntu' option, the USB drive will load the Ubuntu desktop into memory and you can give it a test-drive and see how well your hardware responds. If you are happy that Ubuntu works well enough and all of your hardware is supported adequately; reboot your PC from USB and when it gets to the menu, run the installer to install Ubuntu over the top of OSX if that is really what you want to do!

Oh, and before installing Ubuntu, make sure you take a back-up of any important documents/data that are on your machine as they will be overwritten along with the rest of OSX!

That said, Ubuntu does give you the option to set up dual-boot, so you could try installing Ubuntu alongside OSX. That way you'd have the choice to boot to OSX or Ubuntu.
But I've only set up dual boot once before.... And that was a long time ago and not on a MAC, so I can't remember that much about it! :/