Edit the Bible. It is the information replicated the most times throughout history, and thus it's probably the best vehicle for a cultural or intellectual agenda. Finding the right edits would not be easy, because the bible would need to retain the qualities that made it so viral in the first place.

Edits could include reducing mysogeny/anti-LGBTQ, valuing the happiness and suffering of all beings, and putting more faith in reason. Adding more reason could easily undermine the persuasive power of the bible, but something could probably be done.

The bible was written between 0 and 100 AD in Greek, so "the team" of time travellers would need to learn ancient Greek (the known parts now, all the unrecorded parts when they arrived), go back to either 1 or 2 bc and influence early manuscripts / verbal recitations, or perhaps arrive around 50AD and write the official Bible, or influence those who wrote it.

Since this question didn't get a lot of response on EAF, here's the answer I wrote on LessWrong that I'm moderately proud of:

Broadly, I think I'm fairly optimistic about "increasing the power, wisdom, and maybe morality of good actors, particularly during times pivotal to humanity's history."

(Baseline: I'm bringing myself. I'm also bringing 100-300 pages of the best philosophy available in the 21st century, focused on grounding people in the best cross-cultural arguments for values/paradigms/worldviews I consider the most important). 

Scenario 0: Mohist revolution in China

When: Warring States Period (~400BC)

Who: The Mohists, an early school of proto-consequentialists in China, focused on engineering, logic, and large population sizes.

How to achieve power: Before traveling back in time, learn old Chinese languages and a lot of history and ancient Chinese philosophy. Bring with me technological designs from the future, particularly things expected to provide decisive strategic advantages to even small states (eg, gunpowder, Ming-era giant repeating cross bows, etc. Might need some organizational theory/logistical advances stuff to help maintain the empire later, but possible Mohists are smart enough to figure this out on their own. Maybe some agricultural advances too). Find the local Mohists, teach them the relevant technologies and worldviews. Help them identify a state willing to listen to Mohists to prevent getting crushed, and slowly change the government from within while winning more and more wars.

Desired outcome: Broadly consequentialist one-world government, expanding outwards from Mohist China. Aware of all the classical arguments for utilitarianism, longtermism, existential risks, long reflection, etc.
 

Other possible pivotal points

1. Give power to leaders of whichever world religion we think is most conducive for longterm prosperity[...]
2. [...] (continued on LW)

In general I suspect I might not be creative enough. I wouldn't be surprised if there are many other pivotal points around, eg, the birth of Communism, Christianity, the Scientific Revolution, etc.