OK, so your rpm is up because you are on the gas. Are you flooring it, or on it pretty hard? If you are really pushing the gas hard it will stay in first because the auto has a kickdown, or passing sensor that will drop it down into a lower gear or keep it in low to get the rpm's higher before shifting to keep it in the power band. Does it upshift as soon as you let off the gas? If so, the passing gear could be what's happening. As mentioned before, changing your fluid is a messy job. The only way to make it easier is to install a pan with a drain plug. The filter is going to be right inside your trans after you remove the pan. It is usually silver and flat like a pancake. If you change your fluid, go to an auto parts store and get a replacement filter first, then you will know what it looks like. Some are held in place with a bolt, others just have a push/pull connection that you just pull the filter out and slide another into place.