Here is what I understand.
The OI is the number of contracts sold & bought, change in OI would mean the number of contracts that are either coming new or vanishing from the availability.
So if we say that if for a day change in OI is positive, newer contracts are in action, let's remember contracts start with some one selling and subsequently some one buying it. And that forms a trade or change in OI. If we would have had a good raise in the price of the scrip for that day and there is a good rise in OI for CE options (for a specific strike price) mean there is good build up for the market to go higher than today, vice versa is true for PE options. But beware the converse of increase in price and decrease in OI or vice versa is a reversal sign.
What I am not very sure is about the volume impact on the OI change