Most modern computers can be upgraded quite easily. For example: larger hard disks, more memory or even the latest graphic cards.
It may however be the case in some machines, especially older ones, that they cannot be upgraded. For example machines prior to Pentium II and AMD Athlon based pcs. In these conditions it may be possible to salvage some components from the original machine and build a new one around them.
I can undertake all manner of rebuilds from revamping old pcs to putting together brand new machines.
I can also build machines to customer requirements eg, a simple internet access type right up to a high power games pc.