Editing Sales Tax Rates

Hello,

We have a new sales tax and have two questions-

-We can't seem to edit the actual Sales Tax ID (the first field) when in the Sales Tax Wizard? Where do we find that?

-Is there any way to delete old sales tax records? When we try to delete old records, it says it can't because it is used on an old invoice.

-Lastly is there a way to apply two different tax rates to different items in an invoice?