I purchased Lr 4 back in October of 2012. I recently purchased a new computer and downloaded Lr5 but my serial number won't work now. I was told in a chat I have a cs4 license and it won't work with Lr 5. Do I have to buy another serial number or can I just upgrade???
Serial numbers are specific to a version of Lightroom. A Lightroom 4 serial number will not work with Lightroom 5. Adobe does not sell Lightroom 5 anymore. If that is the version that you think you want then it would be necessary for you to find it from a reseller such as Amazon or B & H Photo, etc. You can purchase Lightroom 6 as an upgrade. But be aware that Lightroom 6 is 64-bit only. You mentioned you were trying to move to Lightroom 5. What are you expecting to accomplish? What are your expectations?