CKEditor current version is v3.6.4-rev7575, and I thought it is time to update the v3.6.2-rev7275 that comes with q2a v1.5.1 / 1.5.2. Changelog here.
Btw, if you do not know what version your editor is, check version number in first line of ckeditor.js.
The downloaded ckeditor zip has a lot of files included, but you just have to copy the following files to your folder "qa-plugin/wysiwyg-editor/" (overwrite the old ones):
Btw, I have not checked the ckeditor's plugins folder one-by-one, just copy all files there as well. Note: At first I tried to keep the old plugins, however, the new version is searching for some language files that are only to find in the new plugin folder.
Hope that helps :)
PS: If you modified the image-dialog (plugins/image) as I once described: Tweaking CKEditor: Do not allow external images, only allow image uploads! you have to add the code for image.js after H.preview.setStyle('display','none');} now.
PS2: I have the feeling that the new version of the editor is a bit faster in opening dialogs.