Dear Gaurav,
to move assets between class, use:
1. Create new assets (AS01);
2. Transfer moviments of the old assets to new assets, and desactive old asset (ABUMN).
Before opening the accounting period in transaction OB52.
However, if many months have passed up (or previous year) is not recommended due to CO.
Other option is:
Consider downloading the assets and enter the new AS91 (with the value of accumulated depreciation).
Good Luck.