Convert Imovie 8.0.6 to 10

Have numerous 8mm tapes. Imported one to iMovie 8. Worked fine. Upgraded to iMovie 10. That first one converted okay. Was going to use 10 for future imports but it does not read most of my tapes. So I use 8. Is there a way to convert these 8 imports to 10? I am wondering about happens if I buy a new computer because that will have the new iMovie on it. I store these iMovie 8 events and projects on an external Seagate drive.

Macbook OS 10.9.4

2.53 Ghz Inter Core Duo

4GB

iMovie 8.0.6

iMovie 10.0.4