Navigate to Admin in your GA4 property, then under Property settings click Attribution settings. You'll see a dropdown to choose from six models: Data-driven (GA4's default), Last click, First click, Linear, Position-based, and Time decay. Select your model and save. The change applies immediately to conversion reporting going forward, but historical data remains attributed under the old model—GA4 doesn't retroactively recalculate past conversions. Data-driven attribution is Google's machine-learning model and typically the best choice if you have sufficient conversion volume (at least 300–400 conversions per month across your key events). It assigns credit based on actual user paths in your data. For lower-volume sites, Last click is simpler and more stable, though it ignores upper-funnel touchpoints. First click favours awareness channels, Linear spreads credit evenly, Position-based gives 40% each to first and last with 20% distributed in between, and Time decay weights recent interactions more heavily. Two things to watch: First, your attribution model only affects conversion metrics shown in the Advertising workspace and attribution reports—it doesn't change the raw event data in Explore or standard reports like Engagement. Second, if you're running Google Ads, your Ads account has its own attribution setting that can differ from GA4's, leading to discrepancies. At Ottawa SEO, we typically stick with Data-driven for e-commerce clients with healthy traffic and Last click for lead-gen sites under 500 conversions per month, where machine learning doesn't have enough signal. We also run periodic Explore reports using different lookback windows (30, 60, 90 days) to validate whether the attribution model aligns with actual customer journeys. If you're switching models, document the change date and expect a discontinuity in your conversion trend lines—don't panic when the numbers shift, it's just a new lens on the same data.