FileDepot upload file sizes restriction
I don't believe that is possible with filedepot without patching the module. However it is readily available within the IMCE module if you are able to change modules.  From the project page:


  
  Basic file operations: upload, delete
  Image(jpg, png, gif) operations: resize, create thumbnails, preview
  Support for private file system
  Configurable limits for user roles: file size per upload, directory
  quota, file extensions, and image dimensions
  Personal or shared folders for users
  Permissions per directory
  Ftp-like directory navigation
  File sorting by name, size, dimensions, date
  Tabbed interface for file operations
  Keyboard shortcuts(up, down, insert(or enter), delete, home, end,
  ctrl+A, R(esize), T(humbnails), U(pload)).
  Built-in support for inline image/file insertion into textareas
  Multiple file selection(using ctrl or shift)
  Ajax file operations
  Themable layout using tpl files
  


For a better idea of what you are looking at, take a look at a screenshot of filedepot.

Everything you need is already built in to IMCE.