I have a network adapter, Realtek RTL8029 (AS) PCI Ethernet, that is limited on downloads from my LAN to 1 mb/s. Is there a way I can unblock it, to make it work at proper speeds?

The slowest ethernet adapter out there is 10 Mbps (original ethernet spec). Are you maybe referring to your broadband internet speeds?

There are no limits on your Ethernet adapter. The only limits would be set by your broadband carrier. To changes those limits you have to pay for a higher tier service if available.

I don't think broadband has anything to do with this. What I mean is with other adapters I can download with speeds like 4, 5 mb / s, while with this adapter I average 800, 900 kb / s. No matter how good the connection with the other user on the network is, I can't go over 1 mb /s. I hope I managed to be clear on this matter.
Thank you for your interest. If you can help, I would thank you some more.

Are you talking about downloads from your internal network?
Are the computers all in the same building connected by ethernet?
How do you gauge "how good the connection with the other user on the network"?

Yes, the computers are all in the same building, connected by a Local Area Network. I don't know exactly what ethernet means but it's included in the name of my adapter.

Sorry about my difficulties in expressing myself. I'm not a computer expert, nor am I a native speaker of English.
Thank you all for your answers.

Check to make sure that you're not hardcoding the network card settings. If you do then you'll need to hardcode the switch to match the speed/duplex of your Ethernet card (i.e. the Realtek RTL8029). Generally the settings should be set to auto speed negotiation and auto duplex negotiation.