You may be able to import from your nulled software as XenForo does have XenForo -> XenForo import facilities but probably not recommended.
Licences are lifetime, support is included for the first year with the licence purchase and any subsequent support can be purchased at the renewal cost.
Generally if you upload the files from the version you're currently running, that should be sufficient. Once the files have been overwritten, you could then try upgrading (if you need a newer version than you have).
Generally if you upload the files from the version you're currently running, that should be sufficient. Once the files have been overwritten, you could then try upgrading (if you need a newer version than you have).
I can't vouch for how the nulled software works, or what people have done to the files you're using. This is why I said; replace all of the files with the proper 1.5.8 files first. As long as that is all working fine, you can then look to upgrading to 1.5.10a. This should just be a normal upgrade; I've never heard of anyone losing data before by doing this from nulled to normal.