boot full

Hello, everyone! I have recently moved my Proxmox PC from the office where I've made the setup. As a consequence, the network where it was connected is no longer available. Today I tried to start the PC, without a network cable attached to it; the result - the boot process got stuck somewhere...

My PC is running out of space with the /boot/ occupied by tenths of linux imanges exeeding roughly 1GB. Is it safe to remove all of them? What is the recommended way to achieve that? I've found some instructions for ubuntu but they seem not to work on PVE. I think it is much safer and better to...