Storing wine bottles horizontally is the preferred method for long-term aging because it keeps the cork moist and in contact with the wine.
This helps to prevent the cork from drying out, which can lead to oxidation.
Before making any changes, carefully inspect each bottle for any visible issues. Check for signs of leakage, unnatural color, cork protrusion, or cork deterioration. If you don't notice any problems, you can proceed.
Transitioning wine from vertical to horizontal storage should not have a negative impact on the wine, especially if it's done carefully and the bottles are in good condition. Once moved, the bottles should be monitored more often than usual, especially for sings of leakage.