Being as collaborative as you can be is a good start. Outside of that, being honest and transparent about why the changes are happening is a good way to build trust with the new team. Keeping a positive attitude and energy around it will also help to soften the blow. Most importantly, continually ask the new team for their feedback along the way. This will help them to understand that while you are implementing new procedures to help things run "your way," you still respect and value their opinion.
Best of luck!
I think the best way to do that would be to sit down with them first to find out what they think is or isn't working and to discuss ways to improve the office. If you can get them involved in the change process you'll get a lot more buy-in. They may even come up with similar or better ideas.
But be sure they understand that while you're allowing it to be a collaborative process, it's you who has to make the decisions and not all decisions will be popular, but they are what's best for everyone in the long run.
First, you need to be crystal clear if the changes to the procedure still supports the policy (or goals) mandated for the organization (ie. Compliance directive, as many HR departments have). If the change impacts this negatively you may want to think twice before moving forward, so as not to put the small business at risk. If ok to move forward, keep in mind procedures are the “recipe for success” that support policy. They are the step-by-step tasks. You don’t mention your level of authority over the acquired small business however the person in charge has every right to direct change. The most simple mentor is to introduce what’s changing, highlight the benefits and say, “effective on such and such a date we will be moving to this new workflow.’ Your procedure should be documented and part of a larger set of documented company assets. It should be easily accessible for all to access. Remembering that change can be difficult for some people you may want to ease into the discussion dropping hints about the benefits of the new method and proposed changes. You’ll also need to ensure training plans are sufficiently in place for a smooth transition. Expect that a smooth transition may take 3 or more weeks depending upon the nature of the change and addition of any tools / additional training req’d. Plan accordingly and be supporting of questions. You can also have some or all of the group pilot a project with the new steps and share feedback. Maybe there’s opportunities to learn from and pick the best of the best between what the staff currently does and what you’re proposing. Be open to learning and sharing for a smoother transition and ‘continuous’ process improvement. Good luck! If you have questions feel free to reach out.
One left-of-centre strategy I've seen is to have employees document one of their work procedures each day in a central, online SOP. Make it really simple & fast to add the procedure.
Next, run a small competition where employees can, with a positive bent, add suggestions for ways that procedures can be streamlined. Have the winner be the person who provides the most, positive, useful feedback that benefits the company.
The best way to change things especially in a new acquired business is to listen and watch. Understanding your team, who they are, and what makes them tick is one of the most influential thing you can do.
Getting their opinion is important, I would construct a model of change and present it as a conversation and get their input. The only way to truly implement your model is to develop a followership before implementing your change strategy.