You could use a DVD to install the OS, either using the inbuilt DVD drive, if it works, or using an external DVD writer.
If it is an old laptop, not the newer UEFI ones, it might support booting an ISO from the HDD. You could use EasyBCD for that. There are other methods of booting an ISO from the HDD, but this one is the easiest.
If your laptop has an HDD, you could switch to an SSD, that will noticeably speed things up.
As for Ubuntu being lighter, I don't know much about that, I haven't used it much, but my understanding is that the antivirus program on Windows makes it slow, while Ubuntu running without an AV runs faster. After a clean install of Windows, my computer runs pretty fast, until I install an AV, at which point it slows down.