In Excel with worksheet displayed:
Select All (Click the square where row and column headers meet)
Hold SHIFT, use menu command Edit -> Copy as Picture (only present when
Shift is used)
Move to a graphics program and Paste as New Image
In Graphics program Save As and specify the format.
These are lots of free graphics programs on the net. but I expect someone
will give you a VBA method that does not need one.
best wishes