There are two ways to delete a field from your query:
Click anywhere in the column and select Edit, Delete Column.
Position the mouse pointer directly above the column, so the pointer turns into a down-pointing black arrow. Then click to select the entire column and press the Delete key; or click the Cut button on the toolbar.
Cut versus Delete
If you cut the column instead of deleting it, you can paste it back into the query. Just select the column where you want it, and then click the Paste button or choose Edit, Paste. Be careful, though; the pasted column replaces the selected one. The selected column doesn't move over ...