No worries - might be worth trying the following:
- Right-click the X86_64 file
- Select Properties
- Click the "Permissions" tab
- Check the "Allow executing file as program" checkbox next to "Execute"
Haven't tried this myself though as I've not got a computer running Linux at the moment
There's also some great advice from Arquivo Morto Games further down in the comments on this page if the above doesn't work
Let me know if you manage to get it up and running