> how do I convert 5.1.1-vi's to 6i? > What do I have to consider?
Just as in previous versions, you simply load the VIs into the new version of LV. The VIs will be converted as they are loaded. Most of them will load with no problems at all. Due to changes in a few features, some of them will bring up a warning dialog telling you that data range checking has changed and may affect execution. Due to name changes in some attributes, a very few VIs can be broken and will require the property to be selected from the menu again.
Its always a good idea to save off a copy of the older VIs, maybe zip up the directory, and put it in a safe place. It should be possible to save the LV6 version of the VIs back to LV5 format, but its best left for a last resort as the roun d trip isn't always symmetric due to all the features that have been added since LV5.