Hi Ratkay,
If I understand correctly, you want to use accounts instead of contacts in the lead process, right?
In first option, it is not enough to just change the main table, there are many mappings in the lead that need to be modified.
In second option, this link only provides a way to unmap the lead name from the contact’s name and replace it with the company name.
In third option, you can try to customize a new Leads table and define its relationship to account table.
In fourth option, business rules can do things like automatically populate fields with conditions you set, but they can't do anything about changing mappings.
Above all, I suggest you try the third options.
