You can do it in several ways, but this may be easiest
1) do a new install on the new server
2) copy the directory /cgi-bin/at3/d/t/ from the old server to the new one
3) chmod all the files you just copied to 777
4) done

This way you copy all trades + stats.
If you want to copy everything, again do a fresh install and copy the entire /cgi-bin/at3/d/ dir.
This way you'll need to go over all paths though, like for the toplist,
since the paths are most likely different on the new server.

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d/t/ contains just the trades database + settings
d/ contains everything, backups, all settings in the script, etc.
However, a lot of settings, like toplists are path-specifc,
so copying everything just like that will create a lot of path errors first.
If you don't mind fixing those, copy everything.