Hi Gina Cyrille ,
It depends where do you want to change the name or alias .
If you would like to change the alias for "Segment"-present in rows ,you cant change the name else you can change different segments inside that segment head .
So it would be really good if you attach twbx file or a screen shot of your worksheet instead of just the name of column or row .
Gina- You won't be able to edit publish data sources/extracts. Unfortunately, this is intentional on Tableau's part to restrict users from editing published data sources. I found this related idea which is still Active and a related thread.
Edit- I had similar issue last week, was trying to edit alias off an extract but it wouldn't let me. Luckily for me, I had the (original) live connection to the server, aliased fields, created an extract again and re-published it.
Hope this helps.