bottom leaves

i wus wondern if any one can answer my ques. i have a few plants and now i am on a 12/12 schedule. the bottom leaves turn yellow and fall off and some are now turning brown on the edges of the big leaves on the bottom. i wus wondering could i start trimming the leaves on the bottom and also the unnecessary ones. would it make a difference if i trimmed them off my self or just let them fall off?. also which leaves could i start to trim cuz thy r really bushy?. thanks
 
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