Currently, I am having Ubuntu 19.10. Trying to upgrade by clicking on the ‘Upgrade’ button, but the button is not working. Please help me. I have high-speed wi-fi also.
looks like 19.10 no longer gets updates: https://itsfoss.com/ubuntu-19-10-end-of-life/
Welcome to ‘It’s Foss’ @Pritam. Go to the site noted by @01101111. It will show you the path for updating. From the site; “If you have a good (internet) speed, consistent internet connection, upgrade to Ubuntu 20.04 from within 19.10. Your personal files and most software remain untouched.”
Also in the future, you might want to stay away from the short term releases and go with a LTS (Long Term Support) release.