OS super slow: what can I do?

I’ve decided to turn an old Compaq Presario V3700 to create a media center with Kodi. Stats: - CPU: Intel Pentium Dual T2410 2 GHz - RAM: 443/971 mb used - SWAP: 1942 - Display: Mobile GM965/GL960 Integrated Graphics Controller (seems to be 2, primary and secondary) - HD: 149.1 G (+ 2 x 931.5G external HD for media storage). More on https://pastebin.com/wf6haWL3

free
              total        used        free      shared  buff/cache   available
Mem:         995224      450560       81964       99960      462700      284572
Swap:       1989628      491776     1497852

The laptop wasn’t doing too bad with Windows. Initially installed Lubuntu, then was advised on the Lubuntu forum to install Ubuntu Server. I did that, it was fun, then installed Kodi. However, the whole machine is just super slow. The boot lasts several minutes, opening Kodi takes 30 seconds or so, and I have to wait several seconds between every mouse / menu selection of Kodi. Movies are also not playing smoothly buy jump frames instead. This is not a Kodi issue though. In the process I installed Firefox to help downloading a couple of things and looking up info, and similarly opening or closing Firefox or a new tab there on can take up to a minute. It’s insanely slow—I feel I’m back in the 2000s. Based on my experience with this laptop with Windows and my past experience with Ubuntu all the way back to 2006 until now, I’m pretty sure this is not normal. So having declared the symptoms, what can I do next? I don’t mind installing any distro that can be of service, so I’m not married to Ubuntu here. Any suggestions?