Issue need help with LVM disk management

[zoldos]

My Plesk server has 2x2TB HDDs. I want to combine these into one 4TB parition without losing my OS or files on Ubunto 16.04. I understand this can be done with my server in "Recovery Mode" and LVM . It is discussed here: How To Use LVM To Manage Storage Devices on Ubuntu 16.04 | DigitalOcean

But it is beyond my skill. Can anyone help, or simply do this for me? lol

Or is this a Ubunto issue, not Plesk? Thanks!