I am trying to update my pi3's systemd version from 215 to the newest build. Does anyone know is this is possible or not? Thank you.
The newest build should be included in one of the repositories. Let's suppose that you are using a raspbian system. First you need to update before getting the upgrade.
sudo apt-get update
If you only want to upgrade your systemd version to the compiled newer one available just select it:
sudo apt-get upgrade systemd
Yes, It Is Possible
While the current version of
systemd in Raspbian Stable (Jessie) is
215-17+deb8u7, there are ways to get newer versions.
Testing Repository (Stretch), Unstable Repository (Sid)
A later version might be available in either the repository for Raspbian Testing (Stretch) or Raspbian Unstable (Sid). Be aware that the newer software is more likely to be less stable:
Older (More Stable) <----------------> Newer (Less Stable) Jessie (Stable) .... Stretch (Testing) .... Sid (Unstable)
You'll have to enable these repository manually. This stackexchange answer looks promising.
Third Party Repository
If the testing version is still too old, there's a chance that some third party offers a newer, compiled and packaged version of
systemd for Raspbian Jessie. You'll have to search the Internet for this.
Be cautious: Like any other software you download from random places on the Internet, there's a chance to get malware on your Pi this way, though I have not heard of such incidents.
Compile From Source
Failing the above, you can compile
systemd from the source code yourself, which is probably quite an involved process.