you can close some background running apps consuming more memory and clear temp files, you can also use document analyzer(Document Analyzer V3.0 Update Available) to analyze your how much memory your objects in app consumes
BTW you can try with removing any unwanted dimension or expression, you should also see if you are using complex expression , if conditions etc. If yes, try to do that calculation in your script and keep your expression as simple as possible.
instead of relying on calculated dimensions, add those condition into the set analysis of expressions, or if you are just modifying the field like grouping or renaming , i suggest you do those at script level.
Try to do most of what you can at script level to take the load off your dashboard