Can the hospital change medical records?

Last april my dad was admitted into the hosptial because of his diabeties. While in the hospital he became unconcious and lost oxygen to his brain and went into a coma. It was said that the nurse gave his too much insulin (which she admitted, but later on denied). Once my dad woke up he had severe brain damage and stayed in the hospital for over 7 months. When the nurses thought he was getting better they moved him out of ICU and into a regular room where he was suppose to be watched 24/7. However, while up there he had a stroke and was sent back to ICU.Also, I believe he had staff. HIs stroke was so severe that it caused his organs to slowly shut down. He passes away oct.29. So , now my family wants to pursue a lawsuit aganist the hospital but we were wondering if the hospital could some how change his medical records to cover themselves so they won't lose the lawsuit.