ms/excell cannot insert pictures

I have an ms/excel 2013 spreadsheet (I am attaching it), that I need to clean and change logos. However all images are locked out and the insert part in the ribbon is greyed out.
what shall I do?

I am attaching a scresshot below

João serras-pereiraAsked:
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João serras-pereiraAuthor Commented:
A comment : it is on the worksheet nr 1 "1 recapitulativo geral"
the workbook is shared.

unshare it and it will work.

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see attached version. i unshared it
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João serras-pereiraAuthor Commented:
Gee... thanks a lot. The only question is... hiw do we unshare? I went to the original file but could find no manner...
how is navigation how to unshare a workbook.

João serras-pereiraAuthor Commented:
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