Place "-1" into an empty cell, copy it, then select your range of positive
numbers and "Paste Special"->Multiply

First, in the future, please ask your question in the body of the post and
only put a short subject in the subject line.............

All I can see of your post is
"How to change positive numbers to negative numbers without re-ente......"

So, to do that,  type -1 in an unused cell somewhere, then highlight it and
do COPY....
Then highlight the cells you wish to change from positive to negative and
then right-click and do PasteSpecial > Multiply............

Vaya con Dios,
Chuck, CABGx3

In  a cell alongside, add

=IF(A1>0,-A1,A1)

and copy down.

Then select column B, Copy, Edit>Pastespecial>Values.

Then delete column A.