Sierra may be rather sluggish on that laptop, with only 4 GB of RAM and a standard hard drive rather than a solid state drive (SSD). If your MacBook Pro is in good shape, you might want to consider upgrading to 8 GB of RAM and a SSD: your lovely, user-upgradable laptop will feel like a new machine. Both upgrades are fairly easy to do yourself. You can find excellent upgrade guides at OWC (macsales.com).
You should not do any major OS upgrade unless you have a complete backup of your system, preferably a bootable clone of your current system. You can use SuperDuper or Carbon Copy Cloner to clone your internal drive to an external drive.
The safest way to apply a major OS upgrade is to install it on a drive other than your current system drive. You could upgrade a clone of your system drive to see whether or not the upgrade will be problematic for your existing system.