Hi, the newest update is V0.5 (Full). As mentioned in the page there are two ways to access Agent Horny.
1. (Patreon) where you can support my project on a monthly basis, download every update from the $5 tier, and get access to Patreon-exclusive perks.
2. (Itch.io) Every update will be released on Itch.io as a separate project on the same day as the $5 tier patreon release. Follow my Itch.io profile to stay up to date. When you pick this option, you get the current and all previous updates. (V0.1-V0.3)
With your purchase of V0.3 you have all the content up until V0.3. For the newer updates you can go with any of the two options.