Two approaches:
1. Hook your phone up to your computer and then cut and paste the appropriate folders from internal storage to external storage.
2. You could also use the My Files app to do the above. Open the app, select Internal storage, click the desired files to be moved or copied, select either copy or move using the upper right icon, then select the SD card as the destination.
The second one is probably the easier one.
If you wish to be careful, you could do a copy and paste and, when you've confirmed the successful move, delete the old files.