Maybe a stupid question, but how can I delete an old project from Premier Elements 13 on Windows 10?
If you did not structure your projects and assets into a specific folder for projects and assets, then you will need to delete the project file (wherever that is saved) as well as all its assets (Auto Saves, Preview Files, Conformed Audio Files, Conformed Video Files). Caution needs to be taken in deleting source media that went into a project since that source media may be being used in another project as well as the one you want to delete.
Best go to the default location
and seek out all the named files specific for the project to be deleted.
Adobe Premiere Elements AutoSave Folder
Adobe Premiere Elements Preview Files Folder
Check Edit Menu/Preferences/Scratch Disks for the location of Media Cache Files (Conformed Audio, cfa and pek)
Check Edit Menu/Preferences/Media for location of Conformed Video Files (mcdb)
Also refer to
Please consider. Any questions or need clarification on the above, please do not hesitate to ask.