That looks like a flower spike so I would leave it to flower then cut the spike down. It may be a yucca of some description rather than a palm. Photo not too clear.
'Optimism is the faith that leads to achievement' - Helen Keller
Your 'palm' is actually not what is seems to be , more likely a Yucca spp. This may sound terribly drastic , but if you want to reduce its size and eventually gain a multi-headed specimen , simply cut the trunk with loppers 3/4 down the trunk , place in dryish location until cut heals over , then place in sunny position and water as normal (I assume it's in a pot) ; side shoots will eventually develop , then grow on as usual .
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That looks like a flower spike so I would leave it to flower then cut the spike down. It may be a yucca of some description rather than a palm. Photo not too clear.
Your 'palm' is actually not what is seems to be , more likely a Yucca spp. This may sound terribly drastic , but if you want to reduce its size and eventually gain a multi-headed specimen , simply cut the trunk with loppers 3/4 down the trunk , place in dryish location until cut heals over , then place in sunny position and water as normal (I assume it's in a pot) ; side shoots will eventually develop , then grow on as usual .