If it's just a general cleanup, you can look at "programs, install uninstall" to see what's installed that you want to remove.
Older laptops with an optical drive, cd rom drive, the optical drive might be in a second bay that can be swapped for a second SATA ssd, in a caddy that fits the optical bay. Older Thinkpads were like that.
Depending on the size of the drive and the workload, the drive could just be too small. Older drive might be 90 gb and that would fill up even with a brand new machine. If you're trying to archive lots of stuff on the laptop, you could try sweeping a lot of that stuff to a USB drive, either a thumb drive or one of the newer portable USB drives that are pcie internally.
New laptop is a good bet. Pace of change has been pretty fast. There are some really nice machines that go on sale regularly. Depending on the workload you could try cleanup or replace the older drive, new ssd's are inexpensive.
If you're putting money into an older machine, a new machine is worth a look, but I would wait. Pick out the machine you want then wait for the sale.