To set the clearance, you use the Electrical Clearance rule in Design>>Rules. Just click on the "10" in the picture shown, and change the value to whatever you want.
The Situs Autorouter will not route with rounded corners. However, you can interactively route with rounded corners. Use Shift+Spacebar to cycle through the various corner modes. You can change the size of the corner by using "," (comma) or "." (period) to decrease or increase. The minimum and maximum values between which you can adjust the corner will be whatever you have set into the design rule for corners.