If you have an ordinary DSL all-hardware phone line modem, it's unlikly that there's anything you can do to make it perform better. You can get firmware updates for older modems which allow some of them that shipped with support for older 56K standards, like X2, to work with the later V.90, if necessary. But apart from that, updates make little difference.
And if you were using host based internal modem, they use the computer's CPU to do the grunt work, instead of having there own on-board hardware. Host based modems, unlike hardware modems, have complicated driver software. Driver upgrades can thus make a significant difference to performance. There are many ways you can tweak the software settings for a modem internet connection. Most of them are a waste of time.
The only modem tweak that does significantly affect both latency and bandwidth is the port speed setting. Port speed is how fast the computer-to-modem connection is over the serial cable. If the port speed is 57600 bits per second, then you have a 56K modem that's connected at a download speed of 48000 bits per second. 56K modems never connect at full speed, and there upload speed is only ever 31200 bits per second, then when you're downloading compressible data with compression turned on your port speed will probably be limiting the speed of your modem.
How much the speed is limited depends on the compressibility of the data you're downloading. Things like GIF and JPG images are basically uncompressible, they're already as small as they can get. HTML and text files, on the other hand, are vary compressible, modem compression can let you double your effective download speed for this sort of content.
Wind up the port speed to 115200 bits per second, and you'll thus see a slight overall bandwidth improvement, thanks to compression. Winding up the port speed will also give you a slight latency improvement, because the faster port speed lets data get into and out of the modem buffers slightly faster.
Edited by Braegnok, 03 November 2016 - 05:12 AM.