Which apps won't it download? My tablet, running 5.1, has no problem with updates (except that it's so slow downloading them that it feels like it's running in geological time...)
I'd expect a 2014 device might have an android 5 update (my Note 10 (2014) got one). Have you tried checking manually for an update via the system update option in the settings? Otherwise you could look at Sammobile.com and see whether there is one (I think you use Odin to install this, but I'm not an expert in updating Samsungs).
I don't hink it likely there will be anything more recent than 5.1 for this device.