Not only are the unevenly laid tiles a sour sight to the eyes, they also pose as a trip hazard. The primary reason of the porcelain floor tiles to be uneven is due to uneven layer of mortar or thinset used to hold the tiles. To make the uneven tiles even, you need to remove the tiles, repair their base and reset the tiles. You would also be required to regrout the tiles. Try to use the grout which matches the existing grout to make the repair work as less obvious as possible.
You should start of by taping the adjacent tiles which you aren’t going to remove. The taping helps to prevent damaging these adjacent tiles. Place the chisel tip along the grout line and tap the chisel with hammer to remove the existing grout around the uneven tiles. Once the grout is cleared, insert the tip of chisel under the uneven tile to pry up the tiles. It is necessary to insert the chisel from the corner to avoid breaking the tiles. Use the scraper to scrape off the mortar from under the tiles that you have removed. Use dry vacuum to sweep away all the debris.
Make another mixture of thinset or mortar and use a trowel to spread it in an even layer under the removed porcelain floor tiles. If you are unable to reach some parts of the opening with a trowel, spread the mortar on the back of the tiles that would be covering the said opening. Place the tiles into position and use any leveling tool to ensure that all the tiles are in level. If required, pull out the tiles and add or remove the mortar as per the need. Finish the process by filling the grout joints.