I have windows seven also I installed Ubuntu 12.04 with Wubi. I haven't had any problem with my 12.04. Now I downloaded 14.04 32 bit and I make my flash boot able with this guide also I uninstall my 12.04 from add or remove program !! (...Wubi make this ability ) Now what next? When I start my computer still I see grub (But I think I should not see that because I uninstall that from win 7 ) also what I should do with my boot able flash- which I installed 14.04 on that- in order to install that. Note My aim is to format windows 7 and 12.04 and just have 14.04 on my computer.
1) Back up your data
2) Place Ubuntu 14.04 on flash drive, hard disk, cd, etc using unetbootin or YUMI (preferrably YUMI)
3) Select your device from boot menu
4) Run and select "Install Ubuntu"
5) Select "Erase disk and install Ubuntu"
or you can also upgrade it to 14.04 first upgrade to 13.04 than 13.10 after tat you would be able to upgrade it 14.04