I can no longer complete downloads

For some odd reason I am not able to download files anymore or rather files greater than +/-20mb. The download process starts fine at the normal speed and then it gradually slows down before the download is complete. I have tried this several times on Chrome and Safari and they both can't complete downloads.

I have scanned my Mac for viruses, i found one, deleted it but things didn't change. Deleted/Unistalled the most recent downloads that were successful and after search forums, searched for Speed Downloader(but I didn't have it). I thought it might be congested ram but i've quit major "memory consuming applications" and just left browsers and nothing helps.

I'm trying to download El Capitan but with this problem, that may take forever.

I'm using a MacBook Pro (13-inch, Late 2011) Yosemite 10.10.5, 2,4 GHz intel Core i5, 4GB 1333MHz DDR3 with 500GB storage space, 100 of which is free.

Please help.