You're going to need to contact Lenovo to find out what CPUs are compatible with your laptop's motherboard and if you will need to do a BIOS update before you upgrade. Then you will need to try and find a compatible CPU. Laptop parts are not sold directly to consumers, only to the laptop manufacturers, which means you are going to have to look around ebay for a used laptop CPU that is compatible with your motherboard. Be aware that the current CPU in that laptop has a TDP of 35 Watts, and any CPU with a higher TDP than that could overwhelm your laptop's cooling system and lead to overheating.
Honestly, even if you do successfully upgrade, do not expect great performance. Mobile CPUs are always much slower than their desktop counterparts, and your upgrade options are all quite old now. At best, you might only get a system that is slightly quicker than your newer Sony Laptop.
I'd say your best bet for now might be to just try running your audio production software on the Lenovo G505, it's probably your fastest laptop all told, and save up some money so that you can build a decent desktop system, or get a much better laptop if you absolutely must have mobility. I doubt it's going to really be worthwhile trying to upgrade your old G550 laptop.