When we mentioned bulk upload, we mean the use of the Salesforce functionality Data Loader.
We use the Data Loader to add, modify, or delete a large amount of records. The upsert wizard combines inserting and updating a record. If a record in your file matches an existing record, the existing record is updated with the values in your file. If no match is found, a new record is created.
Install the Data Loader
a. Go to the Salesforce Setup
b. Navigate for Data management > Data loader or look for "Data loader" in Quick Action
c. Download the relevant Data Loader