For those who are new to Dynamics 365, a few things are possible:
1. You can implement
Microsoft Dynamics 365 Business Central by replacing the existing software.
2. You can implement the new software by keeping the existing software.
3. If you want to implement the new software, but the current system is working perfectly, then you can continue using it and add the new software as another module.
The choice is up to you, depending on your business needs and the status quo of your companies.
