To plot the Density of States (DOS) up to 20 eV, you need to modify your input files to ensure the energy range covers up to 20 eV. First, open the .in1 file and set the energy range line to include values up to 20.0 eV, then save the file. Next, open the .int file and make sure the energy range is also set to 20.0 eV, then save this file as well. Run your DOS calculation using the appropriate commands for your software (e.g., x lapw2 -qtl -up and x lapw2 -qtl -dn for WIEN2k). After obtaining the DOS data, use plotting software such as gnuplot or Python's matplotlib to visualize the DOS up to 20 eV. This ensures your plotted DOS includes the desired energy range.