By default we will only add data to blank fields during an upload. We do not delete existing data if the corresponding field in your upload file is blank. However, if you want to clear out the data you have in existing fields and make it blank you can do that through the advanced upload option 'Clear blank values'. To see this, go to the People menu, select Uploads, then click Add New Upload. In the pop up, click the 'Show all options' button and select 'Clear blank values' in the Other section. You'll only see these options if you have the Advanced Upload permission. When you select this option, we will clear out any data on each matching activist that is blank in your file for columns you decide to match on step 2 of your upload.
So, for example, let's say an activist had a first name in the system, and you uploaded a file with their email address or unique ID but no first name in the first name column. By default, we would keep the first name we have, even though you had a blank space in your file. If you check this box, we will delete the first name value instead, making it blank.
In this way, you can mass-delete values from fields on your activists. Be careful with this option, it cannot be undone.
If your upload has failed for any reason, the administrator who uploaded the file will receive an email notifying them of the issue. This email will contain possible issues with the file and things to try to fix it.
See here for our advanced uploads video tutorial.