how do i erase/delete a large section of my artwork?

Simply draw any kind of mask (rectangular, freehand, whatever) and
press delete. That will "erase" and replace it with the current
background colour.

(If there are objects present, the objects must be selected, and, of
course, not locked, before "delete")

If you need to get rid of it altogether and just keep a portion of the
original, you can crop the entire image with the crop tool (always
rectangular of course).

Hi Steven,

adding to what Paul has said - sometimes, and I have no idea why, making a selection and then hitting delete still deletes the whole object (layer) and not just the part of the object inside the selection. Other times things work as expected and only the selected portion is deleted. If the former happens to you then there is an easy workaround. Undo the delete to get your object back and then select the Eraser Tool. Now hit delete and only the selected part of the object is deleted. Due to this weird peculiarity I have made a habit of always selecting the Eraser Tool before deleting selected areas of an object, just in case.

I just went in and did some testing in X5 and the deleting of a selected portion of an object worked flawlessly without the Eraser Tool being active. It may have been luck, or maybe this issue has been fixed in X5? Either way, at least you know what to do if you find you are erasing entire layers instead of only the selected areas.

Best regards,