Remove Ubuntu partition

[shortanu]

How can I remove Ubuntu after it has been installed as the only partition on a Mb Air?

Need to mention that Ubuntu is not working.

I tried to boot from a USB flash drive with Lion but it does not show the USB when in startup mode.

 

[murphychris]

EFI mode booting supports USB sticks, CSM-BIOS does not. So I'm going to guess that the operating system on the USB stick is not EFI bootable.

For experts, I suggest GPT fdisk which you can find a Mac installer binary at Source Forge. It is not a GUI app, only command line. But with it you can modify GPT partitions to your heart's content, even on a live hard disk - although you should reboot soon after writing out a new GPT. It can also optionally create hybrid MBRs.