Not much instruction needed ... go to ftp://ftp.opera.com/pub/opera/linux/ and download the version you want in one of the "tarball" formats - tar.gz, tar.bz2 or tar.xz. Use whatever archiver you have to extract the file to your home directory. Inside the folder you'll find a shell script that can run Opera without ever installing the file, and also a script that can install the program. If you just run the "opera" script it'll create a "profile" folder within the same folder and run Opera using that profile - which obviously won't overwrite any of Opera 37's files or settings. If you run the install script you can tell the installer where to move the program files (say, to /opt/opera instead of to /usr/lib/opera) - compare that to where Opera 37 is installed and you can again avoid any overwriting.
A few versions of Linux don't use either rpm or dpkg, so they had to have a basic archive with an install script for those versions. The "opera" script was added later so that you could run Opera from the home folder without ever installing it either because you were a user who couldn't get root access to install it properly or because the system had a different version which you ddidn't want to overwrite.