on the upside

It means from a positive point of view. It is always used to contrast to a value neutral or a negative point of view. Here's an example:

Another property tax levy passed, so we'll be paying more in taxes each year. On the upside, we were able to refinance our mortgage at a lower interest rate.

Here, from the narrator's point of view, the higher property tax is a bad thing, because it will have to be paid each year from now on. But getting a new mortgage at a lower rate of interest will save money, so that's a positive thing, that's an "upside" to the situation.

Note the counterpart to "on the upside" which is "on the downside".