What needs to be done to remove a telephone system (PBX)?

I have a phone system that I had leased for my business. The system has a central PBX unit mounted in my phone room, and 5 telephone stations throughout my business.
My lease is expiring at the end of this month and I don’t want to renew it in order to save costs. I have already identified a small telephone system that does not require a PBX but rather plugs into my regular phone lines.
I have 4 telephone lines in my business. What would a technician need to do in order to remove the PBX and return my 4 lines to regular phone lines so that I can use a regular telephone instead of the PBX?