The update route is to move to Adobe Experience Manager. Contact Adobe Sales to obtain Experience Manager.
If you just need to edit the PDF/XDP forms, you should be able to purchase a standalone license for Adobe Forms Designer which will allow you to edit the standalone forms. If you had a previous license of Designer, that should be valid for any future versions of Designer too.
You might need a copy of Acrobat Pro as well so you can reader extend the forms to allow them to continue to be fillable and allow saving.