1. Open Photoshop Lightroom
2. Select an image(s)
3. Go to File > Plug-in Extras
4. Select PhotoFrame
5. The PhotoFrame for Lightroom dialog will appear, select the Open... button.

For Details on using the PhotoFrame for Lightroom dialog look below. 

Tip: If you have multiple images selected and you press the Open...button you will be apply to manually set-up a frame stack for the first image. Each subsequent image in your selection will have the same frame stack applied to it as the first image.

• Search: Type in the name of a preset or favorite frame. The results will appear in the Search Results category. 
• Category List: Lists your preset categories as well as a special category for your Favorites. Click on the triangle to open each category, just like the Library in PhotoFrame.
• Description: Displays the description for the selected preset. You can close this section by clicking on the triangle next to the section title.
• Options: The controls how your image is treated before it is sent to PhotoFrame. You can select from editing the original, a copy with Lightroom Adjustments applied or a just a copy. If you select either of the copy options you may also select the file format, color space and bit depth. If you have multiple versions of Photoshop installed you may also select which version of Photoshop to use PhotoFrame in, or use it as a standalone. The last option, Stack with original will place the edited version of your image in the Lightroom catalog with the original.  You can close this section by clicking on the triangle next to the section title. These settings are remembered.
• Cancel: Cancels PhotoFrame for Lightroom
• Open...: Rather than applying a preset directly, this option will open your image in PhotoFrame so you can manually select the frame(s) and options
• Apply Preset: Applies the selected preset to your image(s)

Note: If you have camera raw files in your selection you will not be able to use the Edit Original option.