The answer depends on whether you arrive from outside Schengen or not, and if you are connecting within Schengen or not. If you give us some more information, I am convinced you could get very detailed step-by-step directions.
But even with the most complicated connection you can come up with, 2.5 hours at ARN will be about twice the time you could possibly need!
Here are SAS estimates:
http://www.flysas.com/en/Travel_info...avel/Transfer/