Is there a way to delete previous years' transactions on my register other than one at a time?

Depends on your profile settings for Notifications in this forum.

Regarding your original question, you can select multiple transactions (just like any other Windows program when selecting a range) and then do Ctrl+D or right click on the selected transactions and select delete from the dropdown list.  Warning, your running balance will no longer be correct unless you change the Opening Balance.

Why do you want to delete your history?  If you were keeping a paper version of your register, would you throw away last year's pages?  If you don't want to see them, use the filter at the top of register and select "This Year" to only display that portion.

If you have investment accounts, you can't delete the history since investments require their history for the # of shares to be correct.