Erik is right - the easiest way is just to choose the next variant up in the family with enough code space!

"(i'm a beginner)"

Hindsight is a wonderful thing and, hopefully, in your next project you will have learned from this experience:

1. The time to start worrying about code space is no later than when you've filled 75% - don't leave it til the last week of your next project!

2. Should you have seen this coming?
ie, now that you've done an 8052 project, can you see that you were cutting it fine trying to fit the whole thing into just 8K?

You should also take the time to review your code: does it really need >8K, or could you have structured and/or optimised it better to fit into the available space?
eg accessing XDATA takes more code than PDATA, which takes more code than IDATA, which takes more code than DATA (using Keil C51 terms); ie the choice of memory location for your variabls can have a significant impact on your code size!

You haven't said whether you where writing in 'C' or assember?