Providing the period isn't locked (for example, you haven't run the year end tool), or it isn't part of a journal you can delete the min bulk by ticking the boxes next to them:
And then click 'Delete Selected'
If you click the top tick box (next to 'Date'), it will tick all of them shown on that page.
Tip: If you want to delete only the untagged transactions, click the red part of the pie chart in the top right first before ticking any boxes