Issue Offloading Apps to Free Up Storage

I need to free up storage to update my iPhone. I am trying to offload Voice Memos, as it takes up almost 1GB, but when I try to offload it, the app still takes up the 868MB or so, even though the download icon is next to it and I cannot open it anymore. The three apps I offloaded previously have the same issue. What is causing this, and how can I actually offload these apps to update iOS?