Branded machines such as HP/Dell/E machines/Acer
Etc., are built to a tight specification to do a set
of tasks- attempting to 'improve' then in anyway will almost certainly lead to a loop of expenditure and frustration, of adding components to a basic machine not designed for them.
Indeed some[Dell] are designed with custom parts that can be virtually -unchangeable.[no ports available]
You may be better advised to work out exactly what you want a machine to do - and seek out a selection of components from the likes of click here
or buy a copy of MicroMart[comes out weekly on a Thursday] and start from the bottom up.