As mentioned for mileage upgrades on Delta you would need to have a Y/B/M fare ticket +25k miles, and also need upgrade inventory availability. DL doesn't sell upgrades for international, so your only other option would be a buy-up from your coach ticket to the current business fare which is likely extremely expensive.

For DL skyclub, you can get a day pass for $50. Not sure if KL sells access for a day or not. Note that if you have a business class ticket, lounge access is included for no charge.

For the KL side, I should note that their procedures are different. In AMS, they often will offer/sell upgrades from coach for a cash copay + miles depending on what fare you have. Its not really publicized so you'd have to inquire at the check-in desk, so best to arrive early for that.