在升级后，需要修改DbContext的配置和连接字符串。具体来说，应该将DbContext的基类从Dbcontext替换为Microsoft.EntityFrameworkCore.Dbcontext，并将options.UseSqlServer方法替换为options.UseSqlServer重新指定连接字符串。示例代码如下：

public class MyDbContext : Microsoft.EntityFrameworkCore.DbContext
{
    public MyDbContext(DbContextOptions options) : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        // Configure your model here
    }
}

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext(options =>
        options.UseSqlServer(Configuration.GetConnectionString("MyConnectionString")));
    // Other service configurations
}