You have a knowledge treasure ready to be mined. Before that you need to integrate, migrate and share your existing knowledge and data with new systems. You have multiple options: extract, transform, load, consolidate, standardize, cleansing, reconcile it.
The systems might show their ages: end of life of products, expiring licenses, unpatched security issues can be fixed with proxy systems or with an Enterprise Service Bus. This can also enable migration of legacy systems.
Migrate Legacy Systems
When some legacy old systems are a technical debt to you: licensing costs too high, vendor lock-in, no security patches, end of life products, hard to find specialists you need to migrate them. Legacy systems can be migrated gradually if you have the knowledge on how to do it surgically. We've done that multiple times. Do it gradually while in total control of your systems.