Feeling slow, Cheap upgrades I should start with??

I recently got my first road bike giant contend 3 (9months ago)on my birthday. Earlier I road a cheap Mtb(200-300USD) for around 4000km doing my first 50km 100km 150km ride.It was obviously a huge leap in performance to entry lvl road bike.

But lately I've gotten used to it and now it feels kinda slow. where should I start with my cheap upgrades??