in the load editor you can use the RENAME statement like this:
RENAME FIELD CREATE_DATE TO [Create Date];
RENAME FIELD ASSIGNED_TO TO [Assignee];
RENAME FIELD CASE_ID TO [Case ID];
RENAME TASK_TYPE TO [Task Type];
The rename will do a rename of a field that occurs in multiple tables too (key fields).
You could alternatively list them all in one statement. Or you could use a map if you have many fields.
Here is the syntax: