Fixing an Unstable Internet Connection
When it comes to your internet connection there are limited things you can do from the software side to improve what you have. This is because software cannot increase bandwidth or lower latency for your existing connection making it a hardware/service issue.
Figuring Out Your Hardware
The main two issues you could have with your existing internet connection are limited bandwidth or an unstable connection with ping spikes. If you are only concerned with gaming, having a slow connection (50 Mbps or lower) is not an issue since for latency-sensitive tasks the stability of your connection is way more important.
If you however have specific workloads that require you to transfer big files over your internet connection or download chunks of data then the opposite is true – you need more bandwidth to get those tasks done quickly.
In both of those cases, the first checks that need to be done are with your modem/router/ethernet cable and motherboard. Using an outdated router or lower Cat cable for your ethernet can cause your speed to be limited to what those parts can handle and not what you are paying for (you pay for 500Mbps but your hardware can handle only 100Mbps).
Most modern motherboards/routers have 1-2.5 Gbps LAN ports and most internet providers when installing your connection will use a Cat 5e at least to make sure any plan that is 1Gbps or under will work perfectly fine.
In the rare case where your motherboard, router, or cable used in your household cannot hold the speed you are paying for you are in for a minor purchase that could resolve your issues. If your demands for your network increase, so will the hardware spending.
Changing Your ISP
The harder thing to do in a situation where your internet connection is not stable enough or does not offer enough bandwidth is to try to find a different ISP that could fix those issues. Depending on their routing and the plans they offer, certain ISPs might be a much better fit for your needs.
The issue with ISPs is that they usually operate in certain regions and you might not be able to sign a contract with them. If your current location is outside of the zone they operate in you might be out of luck and have to deal with the internet connection you have currently.
TL;DR
If your internet is either unstable or has low speeds you need to check if you are bottlenecking your connection with your hardware. If your hardware is up to date then you might need to change to a different ISP if you have the option to.