Ask in the Premiere Pro forum and provide the system specs.
Moving the discussion to Premiere Pro forum.
To adjust the playback resolution:
Go to "Program" (that's the screen where it plays back your video)
Click on the arrow and then select Playback resolution and select Full.
You can render to Full HD by exporting your Media. Choose which format you'd like to export it to & then you have a few presets you can use, also for HD.
When you export, I'd recommend you use Media Encoder, so put it in the queue.
Don't know if this is the best way to do it, but that's how I usually do it
Go to Sequence Settings and adjust your video preview size. Its only adjusting your preview so your output can still be full hd.