So you're saying ...
Amount is now Sum Amount
Name is now Customer Name
Date is now Purchase Date
Removed column is now nothing because it doesn't exist.
You will probably see that the old field names are showing up in red and the new field names are there as well. I usually fix this by right-clicking on the red field name and choosing "Replace References..." and choosing the new field name. This will replace the old field reference with the new field reference and should fix your situation.
If it doesn't work, please let me know
Thanks Chris and Padma, I really presumed this was handled in the data screen rather than through the dimensions and measures but this has sorted the issues pretty quickly!