I'm not sure if I understand you correctly. But the procedure is in dynatrace documentation:
Generally there is migration-tool.jar file which will help you to export configuration from your existing appmon server. Storage and Performance Wherehouse will be the same as for 7.0 so you will not loose your data.
Remember, if you have license with UEM you should deactivate uem voucher in your licenses account and after that license. All steps in proper order ar in link I've provided.
After upgrading Server and Collectors (if they are external, they have to be upgraded manually with using migration-tool.jar as well), agents will connect with 7.2 version automatically.
You have to know as well that default agent technology for 7.2 is Appmon agent (not classic one). Your old system profile will be default configured to be classic one. If you want to move to Appmon agent which gives you more concentrated purepaths with less overhead for you Dynatrace infrastructure, you will have to open extra ports between Agents and Collectors (8043 - SSL and 8042 - non SSL) and between Collector and Server (8041 - SSL and 8040 - non SSL). Appmon agents are using HTTP REST API. Without those ports even if your classic agents are connected properly, collectors will be marked with red light on server settings. I suggest taking care about those ports before migration.