Attention: You need to take care of some things to make v2.x fully work
With v2.0 LiveTraffic becomes compatible with Metal/Vulkan. This is a major change under the hood, affecting some supporting files. Compatibility with X-Plane 10 is dropped, so that LiveTraffic can more easily make use of X-Plane 11's feature, including the installation model.
What you need to do to upgrade from v1.5 to v2.x if you want to keep your current configuration, especially your CSL model setup:
Download the latest LiveTraffic ZIP archive as usual and unpack it.
You will immediately notice the changed folder structure: The actual plugin is now called LiveTraffic.xpl and lives in folders named after the platform: mac_x64, lin_x64, and win_x64.
In your X-Plane installation, go to your existing Resources/plugins/LiveTraffic folder and do some cleanup:
Consider making a backup. Really, think about it...it does have its advantages ;-)
Then actually do it.
Delete the entire 64 folder, which contains the old binaries mac.xpl, lin.xpl, and win.xpl.
Really, remove it. If you keep the 64 folder you might end up running two instances if LiveTraffic.
In the Resources folder, delete lights.png and CSL2XSB.py.
Now copy necessary files from the unpacked ZIP archive:
Copy the mac_x64, lin_x64, and win_x64 folders to your plugins/LiveTraffic folder. They hold the new LiveTraffic plugin binaries.
Copy all 7 files from the Resources folder over to the plugin/LiveTraffic/Resources folder.
You do not need to copy the subfolders ShippedCSL and CSL, they didn't change.
CSL Models: Now, only OBJ8 models are supported. Others are ignored. See Log.txt for not accepted models.
The Bluebell package only consists of OBJ8 models and just works.
X-CSL mostly ships OBJ8, but up to recently had a number of OBJ7 models, which will not be loaded.
Clean up CSL Models
If you never used CSL2XSB.py before, then you're already done!
CSL package conversion with CSL2XSB.py is no longer need. The functionality provided by that script is now built right into LiveTraffic. LiveTraffic will create new copies of the .obj files where and when needed.
The naming of those files created by LiveTraffic is different from the files created by CSL2XSB.py. You may want to remove those old versions just to save on disk space.
Run the provided script RestoreOrig.py, which will remove most of the change done by CSL2XSB.py before. But it cannot remove copies of .obj files created for example for X-CSL models.
For X-CSL: The best way is to start over: Remove all files, download the latest installer, and redownload the models. X-CSL have updated their collection of planes and removed non-OBJ8 planes, so this exercise does make sense. How-to here.
For Bluebell: Just recently (31-AUG-2020) a new release was published. So even for the Bluebells it might make sense to start over and install that fresh release. How-to here.