I have been dealing with resurfacing memories for a long time, so I will add some "technical stuff" to the very good advices given by others on here.
First thing I need to say is : go slow.
Memories of negative events (traumas) are stored in some areas of the subconscious, that the mind "separates" from the main self, by building a mind wall. This happens because traumas may be so severe, that the mind chooses to disconnect the traumatized self, and bury it in the deep subconscious, to continue living. A defense strategy. Amigdala gland is the physical switch to those buried emotions.
To do that, the mind needs to build a main self, dealing with daily life and conscious actions, like a "new person" who lives like nothing bad happened. This main self, constantly puts the emotional buried self down, so it keeps staying buried, using a lot of energies to do that. This is why many traumatized people are often tired, low energy levels, and worried.
I experienced 3 main ways to access buried memories, maybe there are more I don't know. I just relate how it worked for me.
1. Like others said, through meditation while in trance. You can do this by inner dialogue while in trance, you just focus on or call upon "you as a kid" for example, and it may be possible to even talk with this traumatized self buried into the mind.
2. Triggers. If you have been traumatized in a room with the walls painted in blue, just go into a room with the same blue walls, and you may experience flashbacks or intrusive thoughts from the buried emotional selves. A bit difficult to find the right triggers. For me, it was a Demon bringing me to the triggers, so I could remember some facts.
3. Bashing down your main self, that happens while you are very low in your morale or solar energies, basically through a weak 3rd chakra. This is the less advisable way, to me. Just post an anonymous insult to the JoS here as a troll, and you'll be bashed down in a second, by people opposing your will. (partially joking, but works this way).
4. EMDR therapy. I never tried this, but it seems working. It needs to be done by a therapist so... you have also to work on finding a good one and pay him.
Bringing out memories will bring out also negative emotions associated to it. So it is important to go very slow. Anyway, the main self will often oppose to your efforts to bring out painful memories. This may lead to an internal fight and use of high levels of energies. It's a strategy, the brain protects you from too painful memories, so this can prevent your success.
One day I asked my GD : please I want to remember all that happened once for all. Answer was "it's too much for you". Since that day, my GD helped to surface memories slowly, bit by bit.
I suggest to ask for guidance to the Gods here, to define a recovery path. It's too complicated to simply "meditate and emerge", it can lead to insanity, instant suicide, rage outburstts.
Ever heard about those people in the news who - out the blue - kill their families and "they were so kind people" ? Often it comes from uncontrolled emotional surfacing. You may have buried decades of rage... like a dormant volcano.