How to distinguish between change and actual sent amount looking at transaction data
There is no way to know with certainty which output is the actual spend, and which is the change, without being involved in the transaction yourself. It is possible to infer this though, consider the following:

Transaction 'X' has 2 inputs (0.5, 0.5), and 2 outputs (0.7, 0.3). Logically, we can infer that the larger output (0.7) is the spend, because if the spend was the 0.3 output, the user could have saved costs by just using one of the 0.5 inputs to send the transaction. 

However, it is possible for users to purposefully transact in a less efficient way, in order to obfuscate their spending habits, so you can never be absolutely certain.