Unetbootin available for free on windows, mac, and of course linux operating system, on lubuntu unetbootin available on ppa (personal package archives) repository, therefore you need to add the ppa repo first if you want to install it.
Okay, first open up your terminal/console (press CTRL + ALT + T) and then add the ppa repo for unetbootin like this:
sudo add-apt-repository ppa:gezakovacs/ppa
Next, update the repository list by running apt-get update command
sudo apt-get update
Finally, you can install unetbootin using apt-get install command
sudo apt-get install unetbootin
Once installed, you can find unetbootin from the Start Menu > System Tools > UNetbootin. You will get pop-up window asking you to enter root password, so basically you need root permission in order to use unetbootin.
Unetbootin can do two things, first create live usb by downloading the image from list that's provided by unetbootin, second you can create live usb from ISO file that you already have.