Q: upgrade RAM for Macbook Pro mid 2009

These tech Specs say:  MacBook Pro (15-inch, Mid 2009) and (15-inch, 2.53 GHz, Mid 2009) - Technical Specifications

• 4GB (two 2GB SO-DIMMs) of 1066MHz DDR3 memory; two SO-DIMM slots support up to 8GB

But try the -menu System report:

 > About this Mac > System Report > Hardware > Memory.

It should tell you, if your Mac can be upgraded in the Memory section:

My Mac is showing: