The Unblock command is only available when you select a block that has been placed in the document.
Right-click the block you want to unblock.
On the shortcut menu, click Unblock.
After the object refreshes, you can select its elements individually, or you can use a fence to select all elements in the object.
Tip:
If you dragged a .dft, .dxf or .dwg file into the active document and the graphics translated as a single block, you can separate the contents into individual blocks using the Unblock command. This makes the graphics selectable. You can then fence-select elements or objects and drag them to the Block Library File List to create a block file, or you can create master blocks or alternative block views from the graphics using the Block command and the Add Block View command.