I have Ubuntu 14.04 LTS LINUX on an old X61 Thinkpad it runs great for an old Intel dual-core.
A winblows 10 upgrade destroyed the MBR or something.
Install with the Ubuntu live CD and partition the hard drive (or SSD.) You can do a dual boot and keep the Windows 7.
I just upgraded 2 comps in my office to Ubuntu 16.04 LTS -- there were some issues with the installer but it worked out OK. I was looking at a flavor called Ubuntu Mate
https://ubuntu-mate.org/about/
LINUX Mint is a good user desktop friendly GNU/LINUX based on Debian like Ubuntu is.
GNU/LINUX uses maybe 1/2 the hardware resources that the Microcrap Windoz OS requires so older hardware runs like new again.