You have to go through Weaver II first.
See: https://weavertheme.com/upgrading-from-original-weaver-to-weaver-ii/
And: https://guide.weavertheme.com/converting-a-weaver-ii-pro-or-aspen-site-to-weaver-xtreme/
But… that site is not overly complicated. It might be easier to simply do a direct switch to Weaver Xtreme and manually update the basic colors used. There really isn’t that much tricky used as far as I can see.
if there are a lot of per page or per post options used, then the conversion might be more important to use.
It might also be an opportunity to fresh the site and get it a little more modern looking.
But either way will work.