Please visit https://launchpad.net/~lubuntu-dev/+archive/ubuntu/lubuntu-daily. Here you'll find a collection of
ppas (Personal Package Archives) provided by Lubuntu's development team. If you need to know more about ppas, you can look at What are PPAs and how do I use them?. You may also want to know about how to remove a ppa: How can PPAs be removed?.
Now to the specifics ...
The first link I provided offers an Overview of published packages along with a filter: in your case, you'd filter for "Trusty". You'll see that 62 packages are available for Trusty. One of them is
Let's assume you go ahead and install this ppa:
sudo add-apt-repository ppa:lubuntu-dev/lubuntu-daily
You'll then need to run
sudo apt-get update
to update your software sources.
At the next step,
sudo apt-get upgrade
all the existing software on your system will be upgraded to the version offered by the daily ppa, not just
If you really want only lxterminal, you'll need to do a bit more work. You'll need to issue commands preventing upgrading of anything else. And that's covered here: Is it possible to only allow specific packages updates from a PPA.
By the way, since you've mentioned "vivid" in the title of your question, you can run a filter using vivid instead of trusty. As of today, both trusty and vivid have the same version of lxterminal, AFAICT.