Marion Jones -- Sells Tiny TX House ... Buys Not-So-Tiny House

Things are looking up for Marion Jones -- who was infamously stripped of her Olympic gold medals -- because she just traded in her humble Texas home ... for a much nicer version.

In case you didn't already know ... in 2007 Marion -- who was considered a LEGEND in Track & Field -- copped to using steroids throughout her career and as a result was stripped of her medals, lucrative endorsement deals, and thrown in jail on charges of perjury.

But all that's behind her ... Marion and her husband just sold their modest 2,173-square-foot home ... and traded up to a much nicer 3,156-square-foot pad with 4 bedrooms and 2.5 baths ... all for a cool $212k.

With her new crib -- which is just a few miles from the old one -- comes a wooded deck ... 3 living rooms ... a huge master bedroom and a giant back yard where she can run around .

Ya know ... 'cause she's a runner.