due to being an idiot and not thoroughly reading instructions here I am  ...Again

I have DNN 5.2.1 installed. bought some modules from Onyaktech, and the first thing I did was upload Onyaktech Library 6.8

which I now know is not needed. this has caused an error and my site is unavailable right now with a message of

Server Error in '/' Application

Could not load file or assembly 'Telerik.Web.UI' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.IO.FileLoadException: Could not load file or assembly 'Telerik.Web.UI' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Source Error: 

WRN: Assembly binding logging is turned OFF.
To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1.
Note: There is some performance penalty associated with assembly bind failure logging.
To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog].

Onyaktech support said to reinstall my original file of Telerik.Web.UI.dll in the bin folder, and this will fix the issue.

I have found the bin folder and the newly modified Telerik file in it.

So know where do I find the original file, I have looked throughout the file manager and do not see it.

how do I go about replacing it? Copy and paste the whole folder or what?

Also do I need to delete all new files assoc. with Onyaktech Library? If I am asking these questions of course, is this safe for me to do with out destroying something else?

One last thing..I was to amped up and ready to try out some new modules, so of course I forgot to backup the site...like I said...Idiot

Thanks for any help

 William, Thanks for the help. I was able to get to get this to work, I was looking for the "original" install file on my server host account under "file manager". As I have always had my host, install or do updates to my DNN versions I had never DL the DNN community version, so once I did that I was able to replace the Telerik file in the bin folder as mentioned.

The OyaktechLibrary module has been deleted via "host>Module definitions" as mentioned, As far as deleting that way I under stood that previously, I guess my question was that if I didn't need it (or it caused that issue) then I should get rid of it, right?   but now my question is related to your reply of

" Do NOT delete a module by manually removing related files from the file system."

After I have deleted the module via "host>module definitions" but the file is still in the file system when I go to my server account (Powerdnn) >control panel >my domain >file manager >httpdocs >bin and also httpdocs>desktop modules.

Not only are the Onyaktech Library files still there, but also some other modules that I had deleted previously, so is it safe to delete them from file manager now, if not why?

Thanks for your help!