If you are still on Microsoft Dynamics AX 2009, mainstream support for this version is going to end on 4th Oct 2018. This means that if you have not already planned, you need to start planning to migrate to the latest version. Unfortunately, there is no code upgrade path from Dynamics AX 2009 to Dynamics 365 for Finance and Operations, which means that you have to reimplement the customizations in the new version. The silver lining is that there is a data migration tool to assist you with data migration from AX 2009 to Dynamics 365 for Finance and Operations.  

Another approach could be to transition first to Dynamics AX 2012 and then upgrade to the latest version of Dynamics 365 for Finance and Operations. If you have high customizations, this approach can be costly both in terms of money and time and for the same reason not recommended.