Hello.
There are very many ways.
Your DM520 has a "mipsel" chipset - specifically bcm73625 / mips32el. So you have to look for Softcam for the "mipsel" chipset.
It depends on whether you prefer the manual installation procedure - Tutorial : How to install softcam (OSCam/CCCam) manually, if you hate ipk packages (versatile and usable on every Enigma), which depends on the particular chipset architecture. First you have to find the appropriate binary file on the Internet or compile it yourself under Linux.
Or would you prefer an IPK / DEB package for an automated installation for a particular Enigma? Then just get the necessary IPK or DEB package for your Enigma and for your particular chipset.
There is also the option to add another download source to Enigma (if you do not already have one) - for Softcams (including Oscam of course). However, this may depend on the distribution of Enigma (each Enigma may have a different trigger for Softcams if you install it with IPK / DEB packages).
Which exactly Enigma do you use (OpenDreambox, OpenATV, OpenPLi, etc.) ? Your Enigme is just the Dreabox Elite 6.0 ?
Do you know how-to use the terminal / linux shell or in other words the PUTTY application for Windows ?
/////// EDIT :
If you already have Oscam installed and only want to update the oscam binary file (/usr/bin/oscam), you can also use my script. However, Oscam binaries for the feed-servers that are used (see info inside my github script) include Oscam compilations primarily for OE2.0 (for example OpenATV and OpenPLi firmware) and not specifically for OE2.5/2.6 (Dreambox firmware). I can't say for sure if it will work for Dreambox Elite 6.0. It could work. This script only overwrites the binary file downloaded from the feed-server (according to the source http://updates.mynonpublic.com/oea/feed). This my own script should automatically upgrade your binary file (mipsel chipset) automatically:
wget -qO- --no-check-certificate "https://github.com/s3n0/e2scripts/raw/master/oscam-new-version-updater.sh" | bash
If anything does not work, write me a conversation on this forum or write to me on Skype.