cannot upgrade from 16.04lts to 18.04lts; cannot access 'lsb_release'

Hi! wanted to upgrade from ubuntu 16.04.7 LTS to the next LTS (18.04).
SoftwareUpdater would not even start, so Terminal:

sudo do-release-upgrade:

Code:Checking for a new Ubuntu release
Could not load list of meta packages: [Errno 2] No such file or directory: 'lsb_release'
Could not load list of meta packages: [Errno 2] No such file or directory: 'lsb_release'
Traceback (most recent call last):
File "/usr/bin/do-release-upgrade", line 126, in <module>
useProposed=options.proposed_release)
File "/usr/lib/python3/dist-packages/UpdateManager/Core/MetaRelease.py", line 102, in __init__
self.current_dist_name = get_dist()
File "/usr/lib/python3/dist-packages/UpdateManager/Core/utils.py", line 221, in get_dist
universal_newlines=True)
File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
restore_signals, start_new_session)
File "/usr/lib/python3.5/subprocess.py", line 1551, in _execute_child
raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'lsb_release'lsb_release -a
Code:The program 'lsb_release' is currently not installed. You can install it by typing:
sudo apt install lsb-releasesudo apt install lsb-release

Code:Reading package lists... Done
Building dependency tree
Reading state information... Done
lsb-release is already the newest version (9.20160110ubuntu0.2).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.Does anyone know how to fix this or how i can upgrade anyway?
Do you need more information? I don't know what would be relevant in this case.
Thank you in advance!