question goes to lenovo ThinkPad users...
option 1: It is possible to replace the hdd with a new ssd;

option 2: you can install a ssd extra to the existing hdd;
? im confused

Both, depending on the model.
Which series?

ebay -> laptop hdd to ssd -> buy -> screw that shit in -> fuck bitches -> enjoy your fast laptop

some of these steps are optional

Thinkwiki is a good source.
And of course the thinkpad forums, those guys build hybrids from mixed models, fix firmware issues themselves, generally they know more than IBM 😀
I don't know how many thinkpads I own 😛

@nbamaral X230 for example

@jakobev pretty sure it a straight forward replacement, sata3 ssd. Did that on a older x200. No extra disk unless you can use the second pcie slot. Not sure you have room for that.
Check https://forum.thinkpads.com/viewfor...
They are usually very helpful.

@nbamaral thanks for the source. im confused, cause in several videos i watched, they either just replaced the hdd on the side with ssd or opened the notebook and put the ssd under the keyboard..

I don't know x230 that well, but I'd say in that model, lifting the keyboard is the best way to access its guts. If you don't see a drawer on the side or a specific plastic top underneath (one screw, disk symbol) remove just the keyboard screws, and carefully slide it up to the screen direction, lift and disconnect it. Hope this helps :)

@nbamaral yeah for sure, thanks mate

1. Yes you can

2. I use a ThinkPad T470 so yes. I can have an extra SSD in the M.2 slot (2422 and NOT NVMe). And only if you're not already using it for WWAN of course. (Even if you are, you can replace it LOL).