How to Remove Dual Entry in UEFI Boot Menu

I installed Ubuntu 13.10, and it was installed properly. It, however, created two entries in boot menu. Both are named as "ubuntu", and one is not working, which means I can't boot from one "ubuntu" entry. I would like to remove the non-working boot-entry since they have the same name, and I don't know a way to distinguish them in boot menu.

my

$ efibootmgr -L sda

BootCurrent: 0001
Timeout: 0 seconds
BootOrder: 0006,0001,0000,0004,0005
Boot0000* Windows Boot Manager
Boot0001* ubuntu
Boot0004* UEFI: IP4 Realtek PCIe FE Family Controller
Boot0005* UEFI: IP6 Realtek PCIe FE Family Controller
Boot0006* ubuntu

$ efibootmgr -L sda -v

BootCurrent: 0001
Timeout: 0 seconds
BootOrder: 0006,0001,0000,0004,0005
Boot0000* Windows Boot Manager
Boot0001* ubuntu File(\EFI\ubuntu\shimx64.efi)
Boot0004* UEFI: IP4 Realtek PCIe FE Family Controller
Boot0005* UEFI: IP6 Realtek PCIe FE Family Controller
Boot0006* ubuntu (\EFI\Ubuntu\grubx64.efi)

Which entry should I remove? boot0001 or boot0006 ?
Would there be any adverse effects?