Is it possible to upgrade PulseAudio to version higher than 5.0? If yes, then how?
Version 5 is in the Raspbian / Debian Jessie repositories.
Upgrade to Raspbian Stretch and you will get v10.0 Since Jessie has been 'end of life' for quite a while now (with even the successor of Stretch not too far away) I would say this is the best option.
Version 5 of PulseAudio is 2014 vintage (I think), which is fairly old. You didn't indicate which version of Raspbian you are using, but @Dirk has suggested you may be using
Stretch. If that's the case, there are at least two options:
One is as @Dirk suggested: Upgrade your OS to Stretch, and when you install
pulseaudio you'll have ver
10.0-1+deb9u1. You may be able to upgrade to ver 12 on Stretch, but you'll have to install the source, and build it. This may or may not be difficult... you can use Google to do a bit of research, or go to the PulseAudio GitHub page & submit a query.
Another option is to upgrade ver 5 on your current system. As before, you'll probably need to do this by downloading the source code, and building it. Unfortunately, I don't know enough about PulseAudio to tell you whether or not that will break something in your current system, but I will hazard a guess that the package management system will at least warn you before doing something that will make your system unstable.
Let us know if you run into any issues, and we'll try to help further.