You certainly can upgrade its memory. Your model MBP can address a maximum 8 GB.
Other than Apple there are only two vendors with which I have personal experience and can recommend: Crucial and OWC. People have reported problems with many other brands, yet Crucial and OWC's prices are as good as any you are likely to find. You may also find brands recommended by other ASC contributors but I have no experience with them.
Go to Crucial and download the little app that examines your system and recommends RAM upgrade options.
Their prices are good but don't have to buy memory from them - determine what you need and buy it from Crucial or OWC / MacSales. The latter has instructional videos.
The CPU is not upgradable but you might consider replacing the MBP's hard disk drive with a solid state drive (SSD) from OWC. I have purchased many of theirs and have been very pleased with the results. SSD prices have fallen considerably in recent years.
Shop around if you like, but avoid PC-centric vendors. They often sell RAM that won't work on a Mac or SSDs whose firmware is not easily upgraded. OS X upgrades, should you contemplate that, sometimes require corresponding SSD firmware updates.