The most basic of issues in Visio - how do i edit an existing diagram?

[Deleted]

Hi all, our organisation has got Visio online so that i can edit our existing visio diagrams created in 2012. When i open an existing Visio diagram in Visio online, i only have the option to "edit in Visio". Then it says it is opening Microsoft Visio but it does nothing. Can i not edit in Visio online? What am i missing?

Thanks! Anna