That's a good question - for Lenovo. In order to use a replacement processor, it must be socket, board and BIOS compatible. Only the manufacturers of the board can answer these compatibility questions. Usually, manufacturers will have a web page or file that detail the compatible processors. If you cannot find such, you will have to contact their support folks.
My personal thoughts are, (1) It is unlikely that there is any chance of upgrading to a 7 series processor, as most designs are generational, (2) since you have their Core i7 processor offering, I consider it doubtful that there will be any processors available that are an upgrade, (3) since you have a U series processor, it is likely soldered down on the board and cannot be replaced and (4) the cooling subsystem in the laptop is likely designed specifically for this processor and any upgrade would cause either overheating or generate additional blower noise.
All that said, you need to contact Lenovo to find out for sure.
...S
