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Yes, you can cut out the old yellow or brown growth, as this will not grow back. Do not cut any of the green growth.

These articles should be helpful: https://www.gardeningknowhow.com/ornamental/cacti-succulents/scgen/cactus-landscaping.htm
https://www.gardeningknowhow.com/ornamental/trees/sago-palm/how-to-care-for-sago-palms.htm

The sago is an extremely hardy plant and can withstand many conditions, including drought and brief periods of freezes and cold snaps. It’s well suited to both indoor and outdoor environments, can tolerate transplanting, and acclimates well to new environments. This plant is extremely hardy and can survive temperatures ranging from 15-110 degrees F, with special care taken in extreme situations. As tolerant a plant as the sago palm is, sudden extremes in temperature, whether too hot or too cold, can damage the plant—so keep this in mind when you’re placing it in the cactus garden. In fact, you may want to consider growing it in a container where you’ll be able to move it around as needed. The sago palm should be outdoors in partial shade (with three or more hours of sunlight a day) and protected from the wind. Move your palm inside in the fall (before the first frost) and return it outdoors in the spring.

This article will help:
https://www.gardeningknowhow.com/ornamental/trees/sago-palm/prune-sago-palm.htm

It will likely only grow new fronds from the top. If this is not the look that you would like, it would be best to replace it.

This article should help with the whiteflies: https://www.gardeningknowhow.com/plant-problems/pests/control-whiteflies-on-houseplants.htm

Additionally, you can treat the plant with neem oil. Here is more info: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm