You should not delete any valid transactions. Some transactions remain in your list simply because they have not yet cleared the bank. Those transactions must stay. You can delete older transactions that are duplicates or mistakes, but if you want any continuity in your bank reconciliations, even this is not a good idea.
Deletion of transactions going back into prior periods will render all of your bank reconciliation balances as now incorrect. A better solution might be to just create a reversing transaction for each incorrect transaction in your register, and then reconcile them against each other in your next bank rec.
