To switch the storage mode you should change the <AttachmentSaveMode> tag's value in the "web.config" file in EP installation folder from "DataBase" to "LocalDisk" and specify the disk folder in the <DirectoryForStorageFile> tag as follows:
where "C:\epattachments" is the example folder name.
That folder should have full permissions for a user ASP.NET process is run for, e.g. NETWORK SERVICE, or you can set it up for the "Authenticated Users" account.
The structure of projects' and activities' attachments folders is:
Projects' files are located in folders named Project<ProjectID> (i.e. Project1, Project2, etc.).
Activities' files are located in folders named Task<ActivityID> (i.e. Task1, Task2).