Setting generics/parameters in Altera Quartus II
Once you've loaded in your design, analyzes it by clicking the button Start Analysis and Synthesis.
Go to the menu option Assignments > Settings... and click on Default Parameters. You can now set the generics for your entity as you can see from the following screen shot:
Of course you can also use Tcl as we recommend, and include in your synthesis script the following lines
set_parameter -name nbits 4
set_parameter -name maxcount 10