No need to delete them, you can simply ignore these when you map the columns. The important thing is to ensure you have the required columns for the import:
- Date
- Description
- Value (Either as one column or are separate Money In / Money Out)
I would recommend however trying it on an empty bank account first just to be sure it works as expected. It’s much easier to empty a new bank account than one with transactions already in 
[Edit]
This guide may help:
Importing your bank statement