As Community user tagteam pointed out, if you had income and expenditures while operating as a partnership, you are required to file a Form 1065, which for you would also be a final tax return.
When you become a single member LLC, you "default" to a "disregarded entity" (sole proprietorship filing Schedule C on your personal tax return) unless you file an application with IRS to be treated as a corporation (with or without an election to be treated as an S-corp).