Outward leaning culms are very common with smaller (juvenile) bamboo. When the plant is ready (maybe in a year or two) the new culms will be more upright. Pruning out the leaning ones is unlikely to promote new growth. In fact, you will be depriving the plant of leaf mass needed to support overall growth and vigor. I suspect whoever told you that pruning the leaning culms out would promote new, upright growth does not really know a lot about bamboo growth habits. My suggestion: leave the existing growth alone.

However, next spring if you are getting more leaners, you can redirect the growth. Bamboo culms are very pliable when they first come up. You can use twine to pull a culm into a more upright position by putting a loop around it and connecting it to a tall plant stake or to another culm (if that culm is rigid enough). After the new culm reaches its final height it will have "hardened off": you can cut the twine and it should stay erect (unless it's fairly small in diameter and does not have enough rigidity). I've used this successfully even with timber bamboo that send up the occasional leaning culm.