In order to lift a counterbalance lift truck you need to appreciate weight, load centres and centre of gravity position.
The centre of gravity of an unladen counterbalance truck sits at a point directly below the operators seat. This point must align with the centre of the lifting truck or the machine may tip sideways off the forks. The forks should be positioned as wide as practicably possible to reduce the risk of sideways slipping.
A forklift weighs a lot more than is initially apparent. A 2.5t truck typically weighs 4.25t so a 5t truck will be needed to lift it.
Consideration also needs to be given to the load centre. A 2.5t lift truck is typically about 1200mm wide giving it a load centre of 600mm. Given a small undercut to avoid damaging the truck a load centre of 700mm would increase the weight by about 400-500kgs.
Also be aware that electric trucks for example may have motors / gearboxes that extend below the bottom of the truck. Carelessly positioned forks can potentially cause costly damage.
Good luck, Alba Forklift Training