When creating a Lightroom preset, it is saved to a location that all versions of Lightroom share. Therefore, when you install a newer version of Lightroom, presets created in an earlier version are automatically imported.
Note: The setting "Store presets with catalog" in Preferences > Presets causes Lightroom to look for and save your presets to your catalog folder. Enabling this option does not move presets currently in the default folder to the catalog folder. If you have enabled this option in Lightroom and then install a newer version, this preference setting is not passed to the new installation automatically.
Changes in Lightroom between versions can cause some Develop presets created in a prior version to behave in an unexpected manner in a newer version. For example, when you update from Lightroom 3 to Lightroom 4, the default Process Version changes from 2010 to 2012.
If you created a Develop preset in a prior version of Lightroom that saved the Process Version and you would like to update the preset to use the current Process Version, create a preset that incorporates this new setting. Saving over the original preset, while possible, is not recommended as the preset will no longer be usable in the prior version of Lightroom.