It’s pretty easy. You can just find the “Migrate” button when you right click the blueprint, and then transfer it to another folder. If you’re trying to migrate it to another PC,
Migrate it to a new folder (I put mine on my desktop)
Then just copy that to a USB, or fileshare, or zip it and upload it to your email, or put it on your VPS, etc.
Then you just place those files in the content folder of your other project. 
This goes for all content in UE4, not just blueprints.