Honestly, that computer will struggle to do many things, especially web browsing. You could try to install a less demanding web browser like Midori to see if that helps.
Open a Terminal and do one line at a time:
wget https://astian.org/download/midori-browser-for-debian/?wpdmdl=3677
mv index.html?wp* Midori.Appimage
chmod +x *.Appimage
Then just double click on Midori.Appimage to use it.