Let me see if I got this straight. You have two layers of tile on your floor and you prefer the bottom one. You want to remove the top layer?
The chances of this working are between slim and none, and only if the person installing the top layer was totally incompetent.
If the second layer was installed with the correct thinset, just forget it! There's no getting them apart.
When installing one layer of tile over another it is usually recommended to scuff or scratch the bottom layer so there will be better adhesion. If this was done, the bottom layer is ruined anyway.
There are a couple of threads floating around here of people removing carpeting or vinyl and planning on refinishing the hardwood underneath only to find areas of plywood or worse. If the original tile was covered, there is often a reason. Assuming the original tile is all in good condition is dangerous.
IF whoever put the second layer down used the wrong adhesive so it is even able to be pulled apart, and IF they didn't scuff up the old tile, and IF there are no missing original pieces then you would still need to regrout the whole thing.
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