So, if I put a bunch of time into changing the old style.css sheet for my 2.1 installation, can I just change the name of it to k2.css in 2.2 to avoid having to redo all my changes?  Or is the new k2.css stylesheet in 2.2 much different and full of other styles that need to remain for things to display properly.  I suspect this is the case without really investigating it closely. If I can't just replace the k2.css with my old 2.1 style.css, is there another fast way to move my custom css changes from 2.1 to 2.2?  Or do I need to redo it.  Martha

The default style contained within components/com_k2 etc will be overwritten on upgrading.
If you have used the K2 template to be used within your joomla template, templates/joomlatemplate/html/com_k2 etc then this will be saved.

If in doubt, back up first.
If you use cPanel, just navigate to the com_k2 folder and zip it and store it safe, download it.

Although you can use it in V2.2, be aware that there are change between the two so some css will or wont be styled. At this stage, I do not have a list of differences.

If you want more information on K2 templating, then let me know, I can supply links to this on K2Joom.com

Hope that helps.

Simon
K2Joom.com