With an Explorer window open that contains these files,
- Press and release the "Alt" key. This will bring up an extra menu bar at the top.
- Select View -> Details
- Click on the "Size" header at the top of the list. This will sort files by size.
- Single-left-click on the first file in the list to select it.
- Using only the "elevator" scroll at the right of the window, scroll down until the last file that you want in the first group is shown.
- Hold down the Shift key and left-click on this last file. This should select this one and all above it
- Drag these selected files to another folder.
HTH,
JW