How do I change the resolution of circles in Sketchup

From here:

when you first draw a circle, type "48s [ENTER]" for 48 sides. or click on the circle and open the Entity Info dialog box. You can not change the divisions once you pull it to a cylinder though.

Try the 90s rule...

Create a circle by entering 1.0" and press return. Now type 90s & press return. You have created a circle with a diameter of 2", and told Sketchup you want 90 sides. This turns it into a complete circle. You should see the difference. Once you do this, all other circles will have 90 sides, within your current project, regardless of size. It has a memory.

If you export into CAD, you will want to do this 90s with all circles. Otherwise, your CAD (BobCAD) program will likely not recognize it as a circle. This is important for any drill routines, as you will want to place a center dot inside each circle, to specify the drill's (geometry) center location(s).

The "circle" is actually a polygon, and yes, you can specify a higher number of sides. You can type the number value (i.e., number of sides), immediately followed by the letter "s", as in 360s or 1000s, and then hit Enter. While Steve Clayton notes that 90 may be enough sides for even CAD programs to recognize it as a "circle", 360 and above will really represent a really good "circle".