I'm flying to SJO in November and booked the economy standard ticket (not the cheapest light nor the more expensive flex). My outbound flight is via CDG with Air France and inbound flight with KLM via AMS.

I read from the web that KLM doesn't necessarily offer upgrades on their mobile app nor website, even if available. Is this true, do I have to call them or ask for upgrade possibilities at the check-in counter? If not, is there any good estimates when the upgrades are released for sale?