You can't.

You can use letters or numbers or nothing.

Tools|options|General tab|check/uncheck R1C1 Reference style
or
tools|options|view tab|check/uncheck row and column headers.

But there's nothing stopping you from putting headers in row 1 and then freezing
panes so that row 1 is always visible.

As a user of excel, I expect to see the row and column headers.  So I don't see
a problem showing them.  And since many people like A1 reference style and
others like R1C1, I (as a developer) let them see what they want.

If you want to try freezing row 1 so that it's always visible:
Select A1 (to make sure it's visible)
select B1
window|freeze panes.

Every row above the activecell will be frozen.  And every column to the left of
the activecell will be frozen.

hi joe.
sorry. no can do. the default row headers of A, B, C ect can not be replaced
with data headers.
They can be changed to numbers....
Tools>options>general Tab> check R1C1 reference style.
They can be hidden....
Tools>options>view tab>uncheck row and column headers.
but hidding the row headers causes you to loose a lot of functionality.
it would be best to do what most of us do. place our row headers in row 1(i
usually color mine some way) and just deal with/ignore the defalut row
headers.

Sorry
FSt1