I did not find it clear in the rules if a player is required to make conquests on his/her turn. Is it legal to turtle on your turn by not making any actions, redeploying troops and then scoring?
No, it is not required. There's nothing wrong with just leaving everything exactly as is.
Leaving in place one Race token in each Region they occupy, the player may take all his other Active Race tokens from the map back in hand and use them to conquer new Regions.
Note the "may".
The active player can repeat this process to conquer as many new Regions as he wishes during his turn, provided he has enough Race tokens left to accomplish these successive conquests.
"As many new Regions as he wishes." 0 might be as many as you wish.