Lichdom for Warlocks [duplicate]

In our next campaign, I will play a fiend warlock. I have made a pact with a powerful devil. He will get my soul once I die. In exchange, he gave me a portion of his power.
Since the deal, I have matured. I have found religion, and regret the pact. Thus, I want to avoid dying at all cost. My endgoal would be to become a lich (or achieve immortality another way).

Is this even possible for warlocks, or can only wizards become liches? I have read conflicting information online…
How do I go about becoming a lich? Are there fixed rules and requirements, or does my DM have to make it up?