can't upgrade from 18.4 to 18.10

Hello,

I tried to upgrade my ubunto 18.4 to 18.10. At the end, it tells me it cannot continue because I don't have enough disk space on /boot and therefore it did only a partial update. I reboot the system and 18.10 appears, but tells me it is only a partial upgrade because not enough disk space on /boot.

I try to free disk space and get this error:

apt autoremove
E: Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable)
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?

Tried many things, nothing helped, i.e., tried to kill the process, but the process number kept changing and reapearing every time I killed it.

Any suggestions?

Thanks!