Artifacts start at Level 1 with just 1 (or possibly 2) benefits unlocked. You can only level up an individual benefit on an Artifact, not the full Artifact itself. Level Up requires a specific amount of Blueprints and Food, Gold, or Oil per level. The Level Up process is instant and does not take citizens. Level 10 is the current max benefit level. That means that a fully Leveled Up Artifact has all 5 benefits leveled up to 10.