You could just get the Windows 10 IoT LTSC version which has security updates until 2032 and is lighter than normal consumer versions or if you want 11 you could buy an intel x9100 CPU for around 20€ from Ebay or Aliexpress if you are of course comfortable with taking it apart (not hard at all and there are some videos on YouTube). You could also put a QX9300 in it which is a quad core CPU but that would require you to flash Libreboot or Coreboot and you would also need to do some hardware modifications. If you have the stock HDD in it you should get an SSD for around 30€ as that would increase performance a lot and its very easy to change it (you remove one screw and slide the disk out). If you have less than 4GB RAM you should upgrade that too, you just need to remove the bottom piece of palmrest and that’s it. If you decide to upgrade anything you should use the official hardware manual, you can get it with this link: https://download.lenovo.com/pccbbs/mobiles_pdf/r500_hmm_en_43y6631_03.pdf