changing pll settings

Tools -> Chip Editor. You can then double-click on the PLL, which will open the resource property editor, and change its settings. Save it off when you close the floorplanner(it should prompt you). Then run Processing -> Start -> Assembler to create a new programming file, if that's what you want. You could rerun the Timing Analyzer to see what the new timing analysis looks like, the EDA Netlist writer for a new simulation model, etc.

It can be difficult to "find" the PLL in the chip-editor view. Another trick is to right-click it in the Project Navigator Hierarchy(top-left window) and Locate -> Chip Planner.

Note that I believe there was a release of Quartus where you could turn on Smart Compilation, and if the only thing you changed was your PLL settings, then it would just change modify that on the next compile and rerun the assembler/TAN/etc. I don't believe it behaves this way anymore. My best guess is that PLL modifications always change timing, and changing timing technically requires a refit. So the more explicit flow listed above is recommended.