Generally it's impossible (and if it's possible it's a bad idea) to change the processor of a laptop. The only common upgrades are (1) adding RAM or (2) changing the hard disk by a compatible or larger SSD or a larger HDD.
Since you seem to know the model number of the motherboard, please post a link to the specification sheet (for the available interfaces and space) and the processor compatibility list (for choosing the processor).
Hello! Is Aspire 7540G (motherboard jv71tr) compatible with SSD form factor M.2 and with AMD Ryzen 3 1200 or Intel Pentium Gold G5400?