Lets start off focusing on general performance issues:
- Not enough RAM: Many don't have enough RAM for the newer Apps. This system can support 6 GB. I would upgrade it if its still running 2 or 4 GB.
- HD very full and/or highly fragmented: See if you can free up 1/4 of the drive. You may want to think about upgrading it if you still have 120 GB drive. You may want to think about going with a hybrid drive (SSHD) Vs a standard HD drive. The best drive here is: Seagate (500 GB or 1 TB). Your system only offers a SATA I (1.5 Gb/s) so you do need a drive that supports this older standard. This is one of the few that do. Defragmenting is often needed on older systems. You'll need a external bootable drive to do it. If you don't have an external drive I would recommend just replacing the internal drive, as the app you'll need in addition makes it cheaper just replacing the drive. For reference here is the one I use: Drive Genius
- Clean out the old cache & log files. This App makes the job much easier: Disk Doctor or something similar to it.
Once the system is tuned up you should see an improvement. If not then you may have a WiFi connection issue that needs to be diagnosed.
Your system has a 802.11n WiFi adapter so you shouldn't need to replace it.
You may want to check your WiFi routers settings to make sure you are connecting at the ideal frequency. What can happen is the area you live in may have multiple AP's which are stepping on each other which interferes with your throughput. You'll need to get a good WiFi signal monitor like this one: WiFi Explorer it will allow you to see what AP's are near you, then you can alter your WiFi Routers settings so you can move yours to a different range. You also may want to alter your AP's name's so you can isolate out the 2.4 GHz Vs the 5.0 GHz bands. I add the numbers 2 & 5 to my AP's names so I can see them independently.
OK, So you have a SSD installed, in some ways that simplifies things!
No file fragmentation on SSD's so you don't need to worry about that. But you do have to have to be careful on the amount of free space SSD's need a bit more otherwise you'll overwear some of the drive. I strongly recommend you leave 1/3 of the drive free on these smaller drives. Make sure your SSD is rated for SATA I (1.5 Gb/s) otherwise you can encounter issues.
I would still clean out the old cache & log files. As well as tune up the WiFi router so you can get better throughput.