How can I sleep through the night and not wake up at 4am?

Also consider..... If you are waking up at a similar time no matter your stress/worry level or your level or tiredness, consider having a conversation with a sleep specialist. They will go over issues that may be inadvertently impacting your sleep. In the meantime, watch your sleep times, timing of activities and meals before sleep, get regular exercise, ask you doc about medication effects, if any, on your sleep.
Deal with worries. Few adults sleep more than 4 hours in a single chunk before cycling into a lighter stage of sleep.The transition between stages is when many alert, but go back to sleep quickly & forget they woke.If you have pressing concerns or are plagued by the habit of fully alerting, this is a problem.Sleep meds are seldom helpful. Accepting the process as benign & learning to resettle quickly will help.
More to add. What time are you going to bed and how many hours are you sleeping overall? Are there any new stressors? What do you do before bed? As was said before, bedtime routine is very important for a goodnight's sleep, comfortable room temperature; try to avoid tv, caffeine right before bed. Consult with your primary physician and take things from there.