Hi @isabellaharris,
Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you join us.
It's certainly possible to change the colour from light to dark, but it's going to involve a lot of sanding because you can't leave the varnish on.
Varnishes create a sealing coat around the timber that stain cannot penetrate, so to do this we need to remove the varnish.
How To Restore Wooden Furniture is a great article to look to for information.
You'll start by sanding the table back to bare timber. You're going to have to do a lot of sanding, so a random orbital sander is a very good investment. A belt sander would also be handy.
Start with a rough grit like 80 grit to remove the bulk of the material. There's a lot to do, so work in small sections and give your arms a rest often. Once you've gone over everything with the 80 grit, brush the table down and move on to 120 grit then 180 grit and finally 240 grit. Once everything is sanded, brush or vacuum the surface to remove as much sawdust as possible.
Your inspiration image is an extremely dark stain. I'd suggest something like this Sikkens Ebony Cetol HLSe Timber Stain would be close.
Check out How To Stain An Indoor Table for some guidance on staining your table.
Let me know what you think and if you have any further questions, please don't hesitate to ask.
Jacob
