To help us bring you new Confluence Server versions faster, we are considering only providing 64-bit installers. Confluence 5.10 would be the last Confluence release to provide a 32-bit installer.
If you installed Confluence using the 32-bit installer on a 64-bit operating system, you will be able to upgrade using the 64-bit installer.
If you are not able to use the 64-bit installer we'd love to hear from you to better understand how this change would impact you. Please comment on this issue to provide details of your situation for consideration.