You need to be 100% sure that this cell/vob is not used anylonger.
Safe alternative to deleting cell(vob) is to replace cell(all cells in the vob) with "empty" cell (cell that contains only few blank frames).
Start MenuEdit and open vob file;
Select vob/cell you want to delete (selecting vob will delete all its cells);
Note: you may use "Edit" to preview content of the cell to be sure that it is the one you need. Note: check "Show all cells" if you want to see cells without buttons.
Confirm that you really want to delete selected vob/cell;