I was given a spreadsheet of about 1000 leads and contacts. I need to update values such as postal code and was wondering how to best accomplish this. I typically upload leads from an industry event/trade show to the corresponding program in which the leads were obtained from.
Do you mean that the sheet has the new zip codes to update existing leads in Marketo?
You can just import the list as a Static List in Lead Database if these leads aren't members of a program per se.
I would just keep the columns to Email Address | Postal Code
unless you also want to update other fields.