I agree with Pet, the easiest way is the upgrading. As has past some time since the 1.0 version, the forum should have all the answers to your problems in the different upgrades. I should take an upgrade path version to version till 1.5.1. So here you have my little guide:
1- Create a complete backup of your system
2- Restore the backup in a local copy
3- Upgrade to 1.1 (not just overwriting the files, but accessing to the upgrade link)
4- Upgrade to 1.2 (same as above)
5- Upgrade to 1.3 (same as above)
6- Upgrade to 1.4 (same as above)
7- Upgrade to 1.5 (same as above)
8- Upgrade to 1.5.1 (same as above)
9- Create a complete backup of your local copy
10- Restore your local copy backup on your server
If every upgrade is succesfull, you don't have to check the functionalities, because they may have bugs corrected in the next release. You only have to check the 1.5.1 functionalities and check the forum for the patches. Good luck!!