I successfully upgraded my Lenovo G505s-20255 from an AMD A8-4500m to an AMD A10-5750m ES (Engineering Sample). I don't think the AMD A10-4600m will work, because as far as I know, this model has never been sold with this Trinity A10 APU. Therefore I think the BIOS doesn't support it (although the chipset does).
It's also possible to upgrade to the AMD A8-5550m, but that won't be much of an upgrade from an AMD A8-4500m (which is only marginally slower).
https://forums.lenovo.com/t5/Lenovo-3000-and-Essential/G505s-APU-Upgrade-failed/m-p/1551488