Tried the above linky, doesn't work, i get trapped in a doom loop of reentering my details repeatedly . . .
To reduce the size of your mesh, download and install Microsoft 3D Builder. Use it to open your file, then click on the tick to import your file.
Once imported, select 'EDIT' at the top. and then 'simplify'. Use the slider to reduce the number of faces, then click on the tick / 'reduce faces' to actually make the reduction, then save the new version.
EDIT: Cancel the first part of this post, I've managed to download it and get it going. Will report back in due course . . .
cheers,
Robin.