If you are looking to experiment with kits there are three main things you can do, assuming it's one cans or sachets you are using as a base (given there is no need to modify most premium kits since its all in the box).
In order of how easy it is
- Substitute malt extract (either as liquid or dried) for some or all of the sugar if that's what the kit instructions advise. However for light beers, particularly lagers, its sometimes a good idea to leave in some sugar to give the beer a little dryness. For darker beers golden syrup can be used instead of sugar and this brings a subtle taste of its own into the finished beer. GS works well in a stout. You can add brew enhancer but some of these are only a mix of dextrose and dried malt extract so you may as well do that yourself since its cheaper and you will then know what's gone onto your beer
- Next up dry hopping or a hop tea. You can then use a hop of your choice to suit your beer style and this will freshen up the flavour and aroma of the kit. Dry hopping is covered here
https://www.thehomebrewforum.co.uk/threads/a-newbies-guide-to-dry-hopping-your-beer.61045/
and this gives a start on hop selection
https://www.thehomebrewforum.co.uk/...-english-and-american-ales.52909/#post-483777
Hop teas are simply where you infuse some hops in hot (but not boiling water) and then after a good steep add the filtered liquid or the liquid plus hop bits to the beer after the primary has died down
- Last you can use grain to augment a kit using a partial mash. More on that here
https://www.thehomebrewforum.co.uk/threads/simple-kit-plus-mini-mash-method-to-improve-a-kit.52938/
Finally some will advise you change the yeast for a proprietary yeast, but in my experience this is of limited benefit on a beer kit, most kit yeasts are fine, although you could substitute a lager yeast for an ale yeast where this has been supplied with a lager kit as is usually the case, which then allows you to ferment at lower temperatures if you wanted to try that.
