Change of Key in BST

/*
Structure of the binary Search Tree is as
struct node
{
	int key;
	struct node *left, *right;
};
*/
// your task is to complete the Function
// Function is used to change a key value in the given BST
// Note: Function should return root node to the new modified BST
node* insertKey(node *root,int newVal){
    if(root==NULL){
        node *t=new node(newVal);
        return t;
    }
    if(newVal<root->key)
        root->left=insertKey(root->left,newVal);
    else
        root->right=insertKey(root->right,newVal);
    return root;
}
node* minValueNode(node *root){
    node* curr=root;
    while(curr->left!=NULL){
        curr=curr->left;
    }
    return curr;
}
node* deleteKey(node *root,int oldVal){
    if(root==NULL)
        return NULL;
    if(oldVal<root->key){
        root->left=deleteKey(root->left,oldVal);
    }
    else if(oldVal>root->key){
        root->right=deleteKey(root->right,oldVal);
    }else{
        if(root->left==NULL){
            node *temp=root->right;
            free(root);
            return temp;
        }else if(root->right==NULL){
            node *temp=root->left;
            free(root);
            return temp;
        }
        node* temp=minValueNode(root->right);  
        root->key=temp->key;  
        root->right=deleteKey(root->right,temp->key); 
    }
    return root;
}
struct node *changeKey(struct node *root, int oldVal, int newVal)
{
	// Code here
	root=deleteKey(root,oldVal);
	root=insertKey(root,newVal);
	return root;
}