Because of recent changes to WordPress 6.3, there are no old versions of Weaver that work reliably.
If you want to keep using the latest version of Weaver Xtreme (6.3), then you must abandon any older versions. They are likely to crash with PHP errors or WP interface errors.
Often, an old site will work and look okay simply by switching to Weaver Xtreme. You can install the newest version of the theme, pick one of the pre-defined sub-themes, have a look, and revert to the old version if things don’t look okay.
You can read the thread mentioned in the previous answer to this topic, or read a more detailed description in this guide posting:
Converting a Weaver II (Pro) or Aspen site to Weaver Xtreme
If you are really using a very very old version before Weaver II, then your only choice would be to use Weaver Xtreme and start with a sub-theme that is similar to the old one. There are likely to be incompatibilities with old Weaver shortcodes if used.
You can find Weaver II on our Archive pages, but there may be PHP version issues:
Archive Downloads