Membership units in a Limited Liability Company (LLC) can, like stock in a corporation, be transferred from the LLC owners to others, including other current owners of the LLC.
A Sale Agreement or Assignment Agreement can be created to document the transfer of membership units (or stock), the parties to the transfer, the price for the units or stock (if any), etc.
Because of the highly-custom nature of a Sale Agreement, Standard Legal does not offer such a document; see options from other reputable legal companies here.
The LLC Operating Agreement should be modified to reflect any changes in ownership and the transfer of the membership units (or shares if a corporation).
Plus, the Operating Agreement should be reviewed and possibly amended to reflect any changes that the new owners would desire to incorporate or make effective subsequent to the transfer.
If it is easier to create a brand new Operating Agreement (instead of manually revising the original document), see the LLC legal forms option available here.
If the combined process seems too difficult to manage as a ‘do it yourself’ task, Standard Legal always recommends the use of a qualified attorney. Find a local attorney for FREE here.